Testing device and method for simulating loess moisture migration under dry-wet cycle

Abstract

The invention discloses a test device and method for simulating loess moisture migration under a dry-wet cycle. The test device comprises a test box, an environment simulation module, a moisture migration characteristic parameter measurement module and a lost soil particle collection module, the test box is of a three-layer combined structure, and the middle layer is an independent sample groove; 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 nozzle; the temperature simulation unit comprises a heating belt, an air blower, an air inlet pipe, a temperature sensor and an air outlet; the temperature sensor is arranged on the side wall of the upper layer of the test box; the air outlet is formed in the top of the test box; the moisture migration characteristic parameter measurement module comprises a soil moisture temperature sensor, a soil moisture sensor, a soil pressure gauge and a pore water pressure gauge which are buried in multiple layers in the soil sample in the sample groove; the lost soil particle collection module comprises a step-by-step filtering device and a laser particle size distribution instrument. The problem of how to reveal the deep mechanism of the occurrence of loess disasters is solved.

Description

Technical Field

[0001] The present application relates to the technical field of water conservancy engineering, and in particular to a device and method for testing loess moisture migration under simulated dry-wet cycles. Background Art

[0002] Loess, as a soil with special engineering geological properties, has unique physical and chemical properties that make it show an obvious dry-wet alternation state when affected by external factors such as rainfall, evaporation, water diversion and irrigation, and human activities. This dry-wet alternation state not only affects the mechanical properties and structure of loess, but also causes water migration and water redistribution, thereby accelerating the occurrence of disasters in the loess region. The dry-wet cycle refers to the phenomenon of periodic changes in the moisture content of loess due to natural processes such as rainfall and evaporation under natural conditions. In this process, the pore structure, mechanical properties and water migration mechanism of loess will change, and these changes are directly related to the stability and safety of loess. Water migration refers to the process of 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 is also 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 have a more comprehensive understanding of the mechanical properties and structural changes of loess, thereby revealing the deep mechanism of loess disasters, has become a problem to be solved. Summary of the invention

[0004] The embodiments of the present application provide a loess moisture migration test device and method under simulated dry-wet cycles, thereby solving the problem of how to develop a comprehensive test device that can simultaneously simulate dry-wet cycles and moisture migration so that researchers can have a more comprehensive understanding of the mechanical properties and structural changes of loess, thereby revealing the deep-seated mechanism of loess disasters.

[0005] In the first aspect, an embodiment of the present invention provides a test device for loess moisture migration under simulated dry-wet cycles, including a test box, an environmental simulation module, a moisture 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, the upper layer, the middle layer and the lower layer are connected in sequence, and the middle layer is an independent sample slot; the test box has an inner wall and an outer wall; the environmental simulation module includes a rainfall simulation unit and a temperature simulation unit; the rainfall simulation unit includes a main water inlet pipe, a water tank and a rainfall nozzle; wherein one end of the main water inlet pipe is connected to the water tank, and 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 nozzle, a water inlet solenoid valve and a flow sensor are provided on the main water inlet pipe, and a water pump is provided in the water tank; the temperature simulation unit includes a heating element. A tropical zone, a blower, an air inlet pipe, a temperature sensor and an air outlet; wherein, one end of the air inlet pipe is connected to the upper layer of the test box, and the other end is connected to the blower, and a temperature regulating module and an air inlet valve are arranged on the air inlet pipe; the temperature sensor is arranged at the upper side wall of the test box; the air outlet is arranged at the top of the test box; the moisture migration characteristic parameter measurement module includes a monitoring component buried in the soil sample in the sample tank in multiple layers; the monitoring component includes 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 includes a step-by-step filtering device and a laser particle size distribution meter; the step-by-step filtering device includes a plurality of sieves with different apertures arranged at different heights below the sample tank, and the laser particle size distribution meter is externally connected to the step-by-step filtering device to obtain the soil particle loss result.

[0006] In combination with the first aspect, in a possible implementation, it also includes insulation material and steel columns; the insulation material is filled between the inner wall and the outer wall of the test box; the two adjacent sides of the test box are tempered glass, and the tempered glass is provided with a scale for recording the height of the accumulated water; the four steel columns are respectively connected to the combination screw reserved holes on the upper layer, middle layer and lower layer of the test box through a plurality of combination screws and nuts; water sealing rings are installed at the joints of the test box.

[0007] In combination with the first aspect, in a possible implementation, it also includes a gravity sensor; the top of the sample trough is paved with permeable stones, and the bottom of the sample trough is provided with a sieve plate; the gravity sensor is embedded in the bottom of the sieve plate; and geotextiles are laid above the permeable stones.

[0008] In combination with the first aspect, in a possible implementation, the multiple sieves are all pull-out type; the multiple sieves are arranged at different heights below the sample slot in order from large to small apertures; the distances between adjacent sieves are equal; the diameter range of the rainfall holes of the rainfall nozzle is [0.5mm, 1mm].

[0009] In combination with the first aspect, in a possible implementation, the monitoring component is arranged in three layers, each layer is provided with a soil moisture temperature sensor, a soil moisture sensor, a soil pressure gauge and a pore water pressure gauge; similar instruments are arranged in the same column, and the distances between similar instruments in two adjacent layers are equal.

[0010] In combination with the first aspect, in a possible implementation, it also includes multiple branch water inlet pipes; one end of the branch water inlet pipe is connected to the water tank, and the other end extends into the test box through the reserved hole on the lower side wall of the test box, and is located above the multiple screens; the branch water inlet pipes are each provided with a water inlet valve; the number of the branch water inlet pipes is the same as the number of the screens.

[0011] In combination with the first aspect, in a possible implementation, it also includes a wastewater tank and a water outlet pipe; one end of the water outlet pipe extends into the test box through a reserved hole at the bottom of the test box, and the other end is located at the upper end of the wastewater tank.

[0012] In the second aspect, an embodiment of the present invention provides a method for using a loess moisture migration test device under simulated dry-wet cycles, including: measuring the dry density, specific gravity and initial height of a soil sample to be tested; placing the soil sample in a sample trough, and laying permeable stone and geotextile on top of the soil sample; tightly connecting the sample trough to the upper and lower layers of the test box through steel columns, multiple combined screws and nuts to form a complete test environment; burying a soil moisture temperature sensor, a soil moisture sensor, a soil pressure gauge and a pore water pressure gauge in multiple layers inside the soil sample; wherein the soil moisture temperature sensor is used to measure the temperature change in the soil sample in real time, the soil moisture sensor is used to measure the moisture content in the soil sample, the soil pressure gauge is used to measure the pressure distribution in the soil sample, and the pore water pressure gauge is 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 includes: opening the water inlet solenoid valve on the main water inlet pipe, and controlling the water inlet and flow through the flow sensor and the water inlet solenoid valve speed to simulate the rainfall process of the soil sample in the dry-wet cycle; observe and record the change of the water accumulation height in the sample tank until the preset water accumulation height is reached, and then close the water inlet solenoid valve; open the water inlet valve on the branch water inlet pipe to allow the water flow to flush the soil particles on the screen to simulate the flushing effect of rainfall on the soil surface; record the water inlet time after reaching the preset water accumulation height and the time taken for the water accumulation height in the sample tank to drop by a unit height; when the water accumulation height drops to 0, close the water inlet valve on the branch water inlet pipe, take out the screen, and after drying and weighing, combine the analysis results of the laser particle size distribution instrument to obtain the loss results of soil particles; open the air inlet valve on the air inlet pipe and start the heating belt in the test box to simulate the drying process of the soil sample in the field environment; obtain the change of the soil sample weight in real time through the gravity sensor, and when the preset soil sample weight is reached, close the air inlet valve and the heating belt on the air inlet pipe, put the screen back in, and complete the dry-wet cycle steps; calculate the water migration coefficient and water migration rate in the soil sample.

[0013] In combination with the second aspect, in a 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, L is the initial height of the soil sample, for The water level at the time; for The water level corresponding to the moment; calculated according to the formula Calculate the water migration rate in the soil sample; where, is the water migration rate, L is the initial height of the soil sample, is the dry density of the soil sample, is the specific gravity of the soil sample, is the density of water, and t is the time to complete the dry-wet cycle steps.

[0014] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages: The present application embodiment provides a kind of loess moisture migration test device under simulated dry-wet cycle, through the three-layer combined structure of the test box, especially the independent sample slot design, so that the test conditions are closer to the loess layer structure in the actual natural environment, so that the moisture migration process of loess under dry-wet cycle conditions can be more accurately simulated. This design not only improves the accuracy and reliability of the test, but also provides an effective tool for the study of loess moisture migration characteristics. 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 loess moisture migration. The rainfall simulation unit realizes the precise control of rainfall intensity, rainfall time and rainfall pattern 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 coordinated work of the heating belt, the blower, the air inlet pipe, the temperature sensor and the air outlet, and then study the influence of temperature on loess moisture migration. The moisture migration characteristic parameter measurement module can obtain the moisture migration characteristic parameters of loess in the process of dry-wet cycle in real time and accurately through the soil moisture temperature sensor, soil moisture sensor, soil pressure gauge and pore water pressure gauge buried in the sample tank in multiple layers, providing rich data support for analyzing the mechanism and law of loess moisture migration. The lost soil particle collection module can effectively collect and analyze the soil particles lost in the process of loess moisture migration through the combination of step-by-step filtering device and laser particle size distribution analyzer. The step-by-step filtering device separates the lost soil particles according to the particle size through sieves with different apertures, and the laser particle size distribution analyzer can accurately measure the distribution of particles of each particle size, thus providing an important basis for evaluating the degree of loess erosion and formulating effective soil and water conservation measures. It can comprehensively and accurately simulate and study the moisture migration process and characteristics of loess under dry-wet cycle conditions, providing strong technical support for ecological protection and sustainable development in loess areas. It solves the problem of how to develop a comprehensive test device that can simulate dry-wet cycle and moisture migration at the same time, so that researchers can have a more comprehensive understanding of the mechanical properties and structural changes of loess, thereby revealing the deep mechanism of loess disasters. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments of the present invention or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 A schematic diagram of a test device for loess moisture migration under simulated dry-wet cycles provided in an embodiment of the present application; Figure 2A schematic diagram of a combined screw connection provided in an embodiment of the present application; Figure 3 A top view of the test box provided in the embodiment of the present application; Figure 4 A schematic diagram of the three-dimensional structure of the test box provided in an embodiment of the present application.

[0017] Figure 1: 1-test box; 11-sample slot; 111-permeable stone; 112-sieve plate; 2-environmental simulation module; 21-rainfall simulation unit; 211-main water inlet pipe; 212-water tank; 213-rainfall nozzle; 214-water inlet solenoid valve; 215-flow sensor; 216-water pump; 22-temperature simulation unit; 221-heating belt; 222-blower; 223-intake pipe; 224-temperature sensor; 225-air outlet; 226-temperature Degree adjustment module; 227-intake valve; 3-water migration characteristic parameter measurement module; 31-soil moisture temperature sensor; 32-soil moisture sensor; 33-soil pressure gauge; 34-pore water pressure gauge; 4-lost soil particle collection module; 41-screen; 5-insulation material; 6-steel column; 7-combination screw reserved hole; 71-combination screw; 8-nut; 9-gravity sensor; 10-water inlet pipe; 101-water inlet valve; 12-wastewater tank; 13-outlet pipe. DETAILED DESCRIPTION

[0018] In the description of the embodiments of the present application, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, which 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 device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. The terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance. In addition, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0019] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Figure 1 Schematic diagram of a test device for loess moisture migration under simulated dry-wet cycles provided in an embodiment of the present application, as shown in Figure 1 As shown, it includes a test box 1, an environmental simulation module 2, a moisture migration characteristic parameter measurement module 3 and a lost soil particle collection module 4.

[0021] 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 connected in sequence. The middle layer is an independent sample slot 11. The test box 1 has an inner wall and an outer wall. The simulated dry-wet cycle loess moisture migration test device provided in the embodiment of the present application also includes insulation material 5 and steel columns 6. The insulation material 5 is filled between the inner wall and the outer wall of the test box 1. The two adjacent sides of the test box 1 are tempered glass. The tempered glass is provided with a scale for recording the height of the accumulated water. The four steel columns 6 are respectively connected to the combination screw reserved holes 7 on the upper layer, the middle layer and the lower layer of the test box 1 through a plurality of combination screws 71 and nuts 8. Water sealing rings are installed at the joints of the test box 1.

[0022] Furthermore, the design of the test box 1 adopts a three-layer combined structure, namely the upper layer, the middle layer and the lower layer. This design allows the various parts 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 the precise control of the test conditions, but also makes it more convenient to observe and study soil samples at different levels. The middle layer is designed as an independent sample slot 11, which is to accommodate soil samples. The design of the sample slot 11 allows loess samples to be placed separately, which is convenient for various tests and operations. At the same time, the independence of the sample slot 11 also ensures that the soil samples will not be 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 insulation material 5, mainly to maintain the temperature stability in the test box 1 and prevent the external temperature fluctuation from affecting the test results. The addition of insulation material 5 improves the insulation performance of the test box 1, so that when simulating the migration of loess moisture under different environmental conditions, it can be closer to the actual situation. The adjacent two sides of the test box 1 are made of tempered glass. This design allows the state and changes of the loess sample to be clearly observed during the test. At the same time, the scale set on the tempered glass is used to record the height of the accumulated water, which helps to accurately measure and analyze the water migration of loess during the dry-wet cycle.

[0023] Figure 2 A schematic diagram of a combined screw connection provided in an embodiment of the present application, such as Figure 2 As shown, four steel columns 6 are connected to the upper, middle and lower layers 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 various parts tighter, 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. Water sealing rings are installed at the joints of the test box 1 to prevent moisture from leaking from the joints during the test, affecting the accuracy of the test results. The use of water sealing rings ensures the good sealing of the test box 1, making the simulated dry-wet cycle environment closer to actual conditions.

[0024] 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 nozzle 213, wherein one end of the main water inlet pipe 211 is connected to the water tank 212, and the other end extends into the test box 1 through a reserved hole on the upper layer of the test box 1 and is connected to the rainfall nozzle 213. A water inlet solenoid valve 214 and a flow sensor 215 are provided on the main water inlet pipe 211, and a water pump 216 is provided in the water tank 212.

[0025] Furthermore, the main function of the environmental simulation module 2 is to simulate the climatic conditions experienced by loess in the natural environment, especially 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, which is designed to simulate the rainfall process of loess in the natural environment. The main water inlet pipe 211 is a key component connecting the water tank 212 and the rainfall nozzle 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 box 1 through the reserved hole on the upper layer of the test box 1 to ensure that the water flow can smoothly reach the rainfall nozzle 213. The main water inlet pipe 211 is provided with a water inlet solenoid valve 214 and a flow sensor 215. The water inlet solenoid valve 214 is a valve that works on the principle of magnetic force. When the coil is energized, the magnetic material generates suction to attract the iron core to drive the valve body to move, thereby controlling the on and off of the main water inlet pipe 211. In this device, the function of the water inlet solenoid 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 be ensured that the amount of water 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 to help researchers gain a deeper understanding of the water migration characteristics of loess during rainfall. The water tank 212 is used as a water source storage device to provide a stable and sufficient amount of water for rainfall simulation. A water pump 216 is provided in the water tank 212, and the function of the water pump 216 is to pump water out of the water tank 212 and transport it to the rainfall nozzle 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 intensities and durations. The rain nozzle 213 is a key component for simulating rainfall. Its design and distribution are crucial to the uniformity and authenticity of the simulated rainfall. The rain nozzle 213 simulates the rainfall process by spraying water mist or water droplets to ensure that the soil sample can evenly receive moisture. The diameter range of the rain hole of the rain nozzle 213 is [0.5mm, 1mm].

[0026] Specifically, 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, wherein one end of the air inlet pipe 223 is connected to the upper layer of the test box 1, and the other end is connected to the blower 222. A temperature adjustment module 226 and an air inlet valve 227 are arranged on the air inlet pipe 223, the temperature sensor 224 is arranged at the upper side wall of the test box 1, and 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 component buried in the soil sample in the sample tank 11 in multiple layers, and the monitoring component 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 lost soil particle collection module 4 includes a step-by-step filtering device and a laser particle size distribution analyzer. The step-by-step filtering device includes a plurality of sieves 41 with different apertures arranged at different heights below the sample tank 11. The laser particle size distribution analyzer is externally connected to the step-by-step filtering device to obtain the soil particle loss result.

[0027] Further, the temperature simulation unit 22 is intended to simulate the temperature changes experienced by loess in the natural environment. The temperature in the test box 1 is controlled and adjusted to simulate the temperature environment under different seasons or climate conditions. The heating belt 221 generates heat by powering on to heat the inside of the test box 1. The power and temperature of the heating belt 221 can be adjusted as needed to achieve precise control of the temperature in the test box 1. The blower 222 introduces air into the test box 1 through the air inlet pipe 223, and the air inlet pipe 223 is provided with a temperature regulating module 226 and an air inlet valve 227. The temperature regulating module 226 can heat or cool the air entering the test box 1 according to the preset temperature requirements to adjust the temperature in the test box 1. The air inlet valve 227 is used to control the flow rate and speed of the intake air to ensure that the temperature distribution in the test box 1 is uniform. The temperature sensor 224 is arranged at the upper side wall of the test box 1 to monitor the temperature in the test box 1 in real time. Figure 3 This is a top view of the test box 1 provided in the embodiment of the present application, as shown in FIG. Figure 3As shown, the air outlet 225 is arranged at the top of the test box 1, and its function is to circulate the air in the test box 1 to avoid uneven temperature distribution. The moisture migration characteristic parameter measurement module 3 is used to monitor and analyze the microstructure changes and water infiltration characteristics of loess in the process of moisture migration in real time. The soil moisture temperature sensor 31 is used to measure the temperature change in the soil sample in real time. By monitoring the temperature change, the heat conduction and heat convection of the loess in the process of moisture migration can be understood, and then the thermodynamic properties of the loess can be analyzed. The soil moisture sensor 32 is used to measure the moisture content in the soil sample. By real-time monitoring the change of moisture content, the water infiltration and evaporation law of loess in the dry-wet cycle can be revealed, which provides an important basis for analyzing the moisture migration characteristics of loess. The soil pressure gauge 33 is used to measure the pressure distribution in the soil sample. By understanding the change of pressure distribution, the deformation and damage that may occur in the loess during the water migration process can be inferred, which is helpful to predict geological disasters in the loess area. The pore water pressure gauge 34 is used to measure the pore water pressure in the pores of the soil sample. The change of pore water pressure is closely related to the water migration of loess. By monitoring its change, we can deeply understand the water migration mechanism of loess. 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 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 a plurality of sieves 41 with different apertures arranged at different heights below the sample slot 11. The apertures of these sieves 41 are different, and the soil particles lost from the loess sample can be filtered step by step. Through the sieves 41 with different apertures, the lost soil particles can be separated according to the particle size, which is convenient for subsequent analysis and processing. It should be noted that 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 arranged in three layers, and each layer is equidistantly arranged with one of each type of instrument, and the distances of similar instruments in two adjacent layers are equal.

[0028] Figure 4 This is a schematic diagram of the three-dimensional structure of the test box 1 provided in the embodiment of the present application, as shown in Figure 4As shown, multiple sieves 41 are all pull-out type, and multiple sieves 41 are arranged at different heights below the sample slot 11 in order from large to small apertures, and the distances between adjacent sieves 41 are equal. It should be noted that the particle sizes of the sieves 41 are 75μm, 30μm and 5μm from top to bottom. The selection of these particle size limits is based on the particle size classification standards in soil science, which can effectively separate soil particles of different particle size ranges, and then analyze the particle loss characteristics of loess during the dry-wet cycle. Specifically, the 75μm sieve 41 is used to separate powder and sand. In soil science, powder and sand are the two larger types of soil particles, and they play an important role in the structure and properties of soil. Through the 75μm sieve 41, these two types of particles can be separated to provide basic data for subsequent analysis. The 5μm sieve 41 is used to separate powder and clay. Clay particles are the smallest particles in the soil. They have strong viscosity and adsorption, and have a significant impact on the water retention and permeability of the soil. Through the 5μm sieve 41, clay particles can be separated from powder particles, further revealing the loss of clay particles during the dry-wet cycle of loess. The 30μm sieve 41 is set in the middle, and its particle size is the peak of the measured particle size distribution curve. This means that in the loess sample, the number of particles around 30μm is the largest, and it is the main component of loess. Through the setting of this sieve 41, the loss of particles of the main particle size in the dry-wet cycle of loess can be more accurately understood. In addition, according to the specific requirements of the experiment, the setting of the sieve 41 can be increased or decreased. For example, if it is necessary to analyze the loss of particles within a certain particle size range in more detail, the sieve 41 of the corresponding particle size can be added. On the contrary, if particles in certain particle size ranges have little effect on the experimental results, the corresponding sieve 41 setting can be considered to be deleted. The laser particle size distribution instrument is externally connected to the step-by-step filtering device to perform particle size analysis on 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 soil particles can be obtained, and then the erosion and degradation degree of loess in the dry-wet cycle process can be analyzed.

[0029] The loess moisture migration test device under simulated dry-wet cycle provided in the embodiment of the present application further includes a gravity sensor 9, a permeable stone 111 is laid on the top of the sample tank 11, a sieve plate 112 is arranged at the bottom of the sample tank 11, and the gravity sensor 9 is embedded at the bottom of the sieve plate 112. Geotextiles are laid on the top of the permeable stones 111.

[0030] Specifically, the gravity sensor 9 is embedded in the bottom of the sieve plate 112 to monitor the mass change of the loess sample in the sample slot 11 during the dry-wet cycle in real time. When the loess absorbs or loses water, its mass will change accordingly, and this change can indirectly reflect the water migration of the loess. The high-precision measurement of the gravity sensor 9 can capture these subtle mass changes. The permeable stone 111 is laid on the top of the sample slot 11, and its main function is to ensure that water can penetrate into the loess sample evenly. The permeable stone 111 has good water permeability and can make the simulated rainfall or irrigation water evenly distributed on the surface of the loess sample, thereby more realistically simulating the water infiltration process in the natural environment. The sieve plate 112 is set at the bottom of the sample slot 11, and its function is to support the loess sample and prevent particle loss. The aperture selection of the sieve plate 112 has been carefully considered, which can not only ensure the passage of water and fine particles, but also effectively intercept larger soil particles to ensure the accuracy of the test. The particle size of the sieve plate 112 can be set to 2 mm, and of course, it can also be set to other values, and the present application is not limited to the above values. The geotextile is laid on the top of the permeable stone 111, and its main purpose is to prevent the loess sample from leaking sideways or eroding the surface during the test. The geotextile has good filtering and protection properties, can effectively maintain the integrity of the loess sample, and improve the reliability of the test.

[0031] Specifically, the monitoring components are arranged in three layers, each layer is provided 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 row, and the distances between similar instruments in two adjacent layers are equal.

[0032] The loess moisture migration test device under simulated dry-wet cycle provided in the embodiment of the present application also includes multiple branch water inlet pipes 10, one end of the branch water inlet pipe 10 is connected to the water tank 212, and the other end extends into the test box 1 through the reserved hole on the lower side wall of the test box 1, and is located above the multiple sieves 41. The branch water inlet pipes 10 are each provided with a water inlet valve 101, and the number of the branch water inlet pipes 10 is the same as the number of the sieves 41.

[0033] Specifically, the branch water inlet pipe 10 is arranged above the multiple screens 41 to ensure that the water can be evenly and accurately distributed to the loess sample area covered by each layer of filter screen. The branch water inlet pipe 10 corresponding to each layer of filter screen is provided with a water inlet valve 101, which can independently control the water inlet of each layer of filter screen, thereby realizing the precise regulation of the water content of different layers of loess samples. In addition, in order to avoid the accumulation of soil particles leading to inaccurate soil particle size distribution results, the design of each layer of filter screen and the branch water inlet pipe 10 takes into account the permeability and retention of soil particles, ensuring that the soil particles can be effectively separated according to their particle size during the simulation process.

[0034] The test device for loess moisture migration under simulated dry-wet cycles provided in the embodiment of the present application further includes 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 at 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 wastewater discharged from the test box 1.

[0035] The present application embodiment provides a method for using a loess moisture migration test device under simulated dry-wet cycles, including: Determine the dry density, specific gravity and initial height of the soil sample to be tested. Specifically, dry density is the mass of solid particles of the soil sample per unit volume, specific gravity is the ratio of the density of the solid particles of the soil sample to the density of water, and initial height is the original height of the soil sample before the test begins.

[0036] The soil sample is placed in a sample tank 11, and permeable stones 111 and geotextiles are laid on the sample tank.

[0037] Specifically, the arrangement of the permeable stone 111 and the geotextile helps to simulate the soil environment under natural conditions. The permeable stone 111 allows water to pass through while preventing the loss of soil particles. The geotextile further protects the soil sample and ensures its integrity. Such an arrangement can more realistically reflect the water migration of the soil sample during the dry-wet cycle.

[0038] The sample slot 11 is tightly connected to the upper and lower layers of the test box 1 through the steel column 6, a plurality of combined screws 71 and nuts 8, forming a complete test environment.

[0039] The soil moisture temperature sensor 31, soil moisture sensor 32, soil pressure gauge 33 and pore water pressure gauge 34 are evenly buried in the soil sample in multiple layers. 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 pores of the soil sample.

[0040] Perform a dry-wet cycle step. The dry-wet cycle step includes: opening the water inlet solenoid valve 214 on the main water inlet pipe 211, and controlling the water inlet amount 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 dry-wet cycle. Observe and record the changes in the water accumulation height in the sample tank 11 until the preset water accumulation height is reached, and then close the water inlet solenoid valve 214. Open the water inlet valve 101 on the branch water inlet pipe 10 so that the water flow can flush the soil particles on the screen 41, simulating the flushing effect of rainfall on the soil surface. Record the water inlet time after reaching the preset water accumulation height and the time taken for the water accumulation height in the sample tank 11 to drop by a unit height. When the water accumulation height drops to 0, close the water inlet valve 101 on the branch water inlet pipe 10, take out the screen 41, and after drying and weighing, combine the analysis results of the laser particle size distribution analyzer to obtain the loss results of soil particles. The air inlet valve 227 on the air inlet pipe 223 is opened and the heating belt 221 in the test box 1 is started to simulate the drying process of the soil sample in the field environment. The weight change of the soil sample is obtained in real time through the gravity sensor 9. When the predetermined weight of the soil sample is reached, the air inlet valve 227 and the heating belt 221 on the air inlet pipe 223 are closed, and the screen 41 is put back to complete the dry-wet cycle step.

[0041] Specifically, the dry-wet cycle step simulates the moisture change process of soil samples in the natural environment. By controlling the water inflow, flow rate and drying conditions, the moisture migration and soil particle loss of soil samples in the dry-wet cycle can be simulated, so as to gain a deeper understanding of its moisture migration characteristics. The moisture migration coefficient and moisture migration rate in the soil sample are calculated.

[0042] According to the formula Calculate the water migration coefficient in the soil sample. Where k is the water migration coefficient of the soil sample, L is the initial height of the soil sample, for The water level corresponding to the moment. for The water level corresponding to the moment.

[0043] Specifically, the constant 2.3 in the water migration coefficient in the soil sample is derived based on experience.

[0044] An embodiment is listed below to illustrate the process of calculating the water migration coefficient in the soil sample. Of course, other embodiments are also possible, and the present application is not limited to this embodiment.

[0045] Assume that in the dry-wet cycle test, the initial height L of the soil sample is 10 cm. After the test starts, the following data are recorded: = 1 hour, water level is 8cm. = 3 hours, water level Reduced to 4cm. First calculate the absolute value of the time difference: hours, and then calculate the logarithm of the relative change in water height: , substitute all known values ​​into the formula .

[0046] Furthermore, when the k value is large, it means that the soil sample has experienced a large amount of water migration in a short period of time, that is, the water migration rate is fast or the migration ability is strong. When the k value is small, it means that the soil sample has less water migration in the same period of time, that is, the water migration rate is slow or the migration ability is weak. The change of k value can reflect the water migration characteristics of soil samples under different conditions, such as migration behavior under different soil types, different humidity conditions or different environmental factors.

[0047] Calculated according to the formula Calculate the water migration rate in the soil sample. is the water migration rate, L is the initial height of the soil sample, is the dry density of the soil sample, is the specific gravity of the soil sample, is the density of water, and t is the time to complete the dry-wet cycle steps.

[0048] An embodiment is listed below to illustrate the above process of calculating the water migration rate in the soil sample. Of course, other embodiments are also possible, and the present application is not limited to this embodiment.

[0049] Assume the following data: the initial height L of the soil sample is 10 cm, the dry density of the soil sample is 1.6g / cm 3 , the specific gravity of the soil sample is 2.7, the density of water 1g / cm 3 The time t to complete the dry-wet cycle step is 24h.

[0050] Substitute all known values ​​into the formula In this embodiment, the unit of the calculated water migration rate in the soil sample is cm / h, which can be converted into millimeters per day (mm / d). Since 1cm=10mm, 1h= day, so 1cm / h=10× mm / d= mm / d.

[0051] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other. Each embodiment focuses on the differences from other embodiments.

[0052] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit the present application. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, 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 test device for loess moisture migration under simulated dry-wet cycles, characterized in that: It comprises a test box (1), an environmental simulation module (2), a water migration characteristic parameter measurement module (3) and a lost soil particle collection module (4); The test box (1) is a three-layer combined structure, divided into an upper layer, a middle layer and a lower layer, the upper layer, the middle layer and the lower layer are connected in sequence, and the middle layer is an independent sample slot (11); The test box (1) has an inner wall and an outer wall; The environmental simulation module (2) comprises a rainfall simulation unit (21) and a temperature simulation unit (22); The rainfall simulation unit (21) comprises a main water inlet pipe (211), a water tank (212) and a rainfall nozzle (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 box (1) through a reserved hole on the upper layer of the test box (1) and is connected to a rainfall sprinkler (213); a water inlet solenoid valve (214) and a flow sensor (215) are provided on the main water inlet pipe (211), and a water pump (216) is provided in the water tank (212); 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 in communication with the upper layer of the test box (1), and the other end is in communication with the blower (222); a temperature regulating module (226) and an air inlet valve (227) are provided on the air inlet pipe (223); The temperature sensor (224) is arranged on the upper side wall of the test box (1); The air outlet (225) is arranged at the top of the test box (1); The water migration characteristic parameter measurement module (3) comprises monitoring components buried in multiple layers inside the soil sample in the sample slot (11); The monitoring component comprises a soil moisture temperature sensor (31), a soil moisture sensor (32), a soil pressure gauge (33) and a pore water pressure gauge (34); The lost soil particle collection module (4) comprises a step-by-step filtering device and a laser particle size distribution analyzer; The step-by-step filtering device comprises a plurality of screens (41) with different apertures arranged at different heights below the sample tank (11); a laser particle size distribution meter is externally connected to the step-by-step filtering device to obtain soil particle loss results.

2. The loess moisture migration test device under simulated dry-wet cycle according to claim 1, characterized in that: It also includes thermal insulation material (5) and steel columns (6); The thermal insulation material (5) is filled between the inner wall and the outer wall of the test box (1); The two adjacent sides of the test box (1) are made of tempered glass, and the tempered glass is provided with a scale for recording the height of the accumulated water; The four steel columns (6) are respectively connected to the combination screw reserved holes (7) on the upper layer, the middle layer and the lower layer of the test box (1) through a plurality of combination screws (71) and nuts (8); Water sealing rings are installed at all joints of the test chamber (1).

3. The loess moisture migration test device under simulated dry-wet cycle according to claim 1, characterized in that: Also included is a gravity sensor (9); The top of the sample trough (11) is paved with permeable stones (111), and the bottom of the sample trough (11) is provided with a sieve plate (112); The gravity sensor (9) is embedded in the bottom of the sieve plate (112); Geotextiles are laid on the top of the permeable stones (111).

4. The loess moisture migration test device under simulated dry-wet cycle according to claim 1, characterized in that: The plurality of screens (41) are all of a pull-out type; A plurality of sieves (41) are arranged at different heights below the sample tank (11) in order of aperture from large to small; The distances between adjacent screens (41) are all equal; The diameter range of the rainfall hole of the rainfall nozzle (213) is [0.5mm, 1mm].

5. The loess moisture migration test device under simulated dry-wet cycle according to claim 1, characterized in that: The monitoring components are arranged in three layers, each layer being provided with a soil moisture temperature sensor (31), a soil moisture sensor (32), a soil pressure gauge (33) and a pore water pressure gauge (34); Instruments of the same type are placed in the same row, and the distances between instruments of the same type in two adjacent layers are equal.

6. The loess moisture migration test device under simulated dry-wet cycle according to claim 1, characterized in that: It also includes a plurality of branch water inlet pipes (10); One end of the water inlet pipe (10) is connected to the water tank (212), and the other end thereof extends into the test box (1) through a reserved hole at the lower side wall of the test box (1), and both are located above the plurality of screens (41); Each of the branch water inlet pipes (10) is provided with a water inlet valve (101); The number of the branch water inlet pipes (10) is the same as the number of the screens (41).

7. The loess moisture migration test device under simulated dry-wet cycle according to claim 1, characterized in that: It also includes a waste water 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 at the bottom of the test box (1), and the other end is located at the upper end of the waste water tank (12).

8. A method for using a loess moisture migration test device under simulated dry-wet cycles, characterized in that: The loess moisture migration test device under simulated dry-wet cycle as claimed in any one of claims 1 to 7 comprises: Determine the dry density, specific gravity and initial height of the soil samples to be tested; Put the soil sample into the sample trough (11), and lay permeable stone (111) and geotextile on the sample trough (11); The sample tank (11) is tightly connected to the upper layer and the lower layer of the test box (1) by means of a steel column (6), a plurality of combination screws (71) and nuts (8) to form a complete test environment; A soil moisture temperature sensor (31), a soil moisture sensor (32), a soil pressure gauge (33) and a pore water pressure gauge (34) are evenly buried in multiple layers inside a soil sample; wherein 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; Performing wet-dry cycle steps; The dry-wet cycle step comprises: Opening the water inlet solenoid valve (214) on the main water inlet pipe (211), and controlling the water inlet amount 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 dry-wet cycle; Observe and record the change in the water accumulation height in the sample tank (11), and when the water accumulation height reaches a preset level, close the water inlet solenoid valve (214); Opening the water inlet valve (101) on the water inlet pipe (10) to allow water to flush the soil particles on the screen (41) and simulate the flushing effect of rainfall on the soil surface; Recording the water inflow time after reaching a preset water accumulation height and the time taken for the water accumulation height in the sample tank (11) to drop by a unit height; When the water level drops to 0, the water inlet valve (101) on the water inlet pipe (10) is closed, the sieve (41) is taken out, and after drying and weighing, the loss result of soil particles is obtained in combination with the analysis result of the laser particle size distribution instrument; Opening the air inlet valve (227) on the air inlet pipe (223) and starting the heating belt (221) in the test box (1) to simulate the drying process of the soil sample in a field environment; The weight change of the soil sample is obtained in real time by means of a gravity sensor (9); when the weight of the soil sample reaches a predetermined weight, the air intake valve (227) and the heating belt (221) on the air intake pipe (223) are closed, and the screen (41) is re-inserted to complete the dry-wet cycle step; Calculate the water migration coefficient and water migration rate in the soil sample.

9. The method for using the loess moisture migration test device under simulated dry-wet 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, L is the initial height of the soil sample, for The water level at the time; for The water level at the time; Calculated according to the formula Calculate the water migration rate in the soil sample; where, is the water migration rate, L is the initial height of the soil sample, is the dry density of the soil sample, is the specific gravity of the soil sample, is the density of water, and t is the time to complete the dry-wet cycle steps.

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