Test device and method for indoor simulation of freeze-thaw cycle of seasonal frozen river slope

Abstract

The invention discloses a test device and method for freezing and thawing cycle indoor simulation of a seasonal frozen river slope, and belongs to the technical field of river dynamics. The device comprises a test box body, an environment temperature adjusting assembly and a plurality of data acquisition assemblies; a soil body layer for simulating a side slope and a water body for simulating a river are accommodated at the inner bottom of the test box body; the environment temperature adjusting assembly is arranged at the top of the test box body, and a water inlet pipe and a water outlet pipe which extend into the box body are arranged on the test box body; the plurality of data acquisition assemblies are distributed in the soil body layer, in the water body, in the sample box body and / or outside the test box body; the bottommost part of the soil body layer extends below the water body; a waterproof heating piece is arranged on the contact interface of the soil body layer and the bottom of the water body; the heating piece and the environment temperature adjusting assembly are independently adjusted. In the water body freezing stage and the stable freezing stage, the heating piece can start heating. According to the invention, the freezing and thawing cycle process of the seasonal frozen river slope can be accurately simulated.

Description

Technical Field

[0001] The invention belongs to the technical field of river dynamics, and in particular relates to a test device and method for indoor simulation of freeze-thaw cycles of seasonally frozen river slopes. Background Art

[0002] In high-latitude regions, rivers freeze during low winter temperatures, then melt in spring when temperatures rise, creating a cycle of freeze-thaw cycles. This freeze-thaw cycle significantly impacts the soil properties of river slopes. For example, the thawing process causes a decrease in soil moisture content and a rapid drop in groundwater levels, leading to slope instability and bank collapse. Statistics show that freeze-thaw-induced slope instability in Northeast and Northwest my country results in hundreds of millions of yuan in economic losses each year, impacting the stable operation of water conservancy infrastructure and the safety of life and property of residents along the river.

[0003] Traditional slope stability analysis is often based on static conditions, usually assuming that the soil is in a stable mechanical state. It ignores the internal moisture migration, temperature changes and the resulting changes in soil structure during the freeze-thaw cycle, making it difficult to accurately reflect the impact of the dynamic process of freeze-thaw cycles on the mechanical properties of slope soil.

[0004] Existing test devices have many flaws when simulating freeze-thaw cycles. For one thing, most simulations generalize the distribution of water in the soil during the freeze-thaw process to a uniform distribution, ignoring the effect of river water levels (water pressure) on the seepage of slope soil. In natural environments, changes in river water levels create a water level difference with the groundwater level on the slope, generating seepage, which will change the saturation and pore water pressure distribution of the soil, thereby affecting the stability of the slope. However, existing devices have not yet been able to effectively simulate the fluctuations in river water levels and the changes in groundwater levels on the slope simultaneously, resulting in significant deviations from the actual situation. Furthermore, existing devices do not fully consider the water stratification of seasonally frozen rivers, where the surface water is frozen and the lower layer remains free water. This water stratification phenomenon creates unique temperature fields and hydraulic conditions, affecting the stability of slope soil. Because existing devices are unable to accurately simulate these issues, the experimental simulation accuracy is low and it is difficult to monitor soil parameters in real time, which restricts research on the stability of seasonally frozen river slopes.

[0005] In terms of freeze-thaw process implementation, existing studies can only roughly control the overall temperature of the soil, and cannot accurately simulate the temperature changes of the soil at different depths. It is also difficult to control the freezing depth and temperature stratification of the water body. The water body is completely frozen or evenly heated during the test. For example, the freeze-thaw cycle chamber developed by the University of Waterloo in Canada can achieve shallow freezing through dual-temperature zone control, but its refrigeration system has high energy consumption and cannot simulate dynamic changes in water level. In terms of water level control, existing test systems mostly control temperature and water level independently, lack a dynamic regulation mechanism for the coordinated temperature-water level-seepage field, and key parameters such as the water level change rate and temperature gradient cannot achieve nonlinear time series matching, and cannot accurately simulate seasonal and sudden changes in river water levels. These deficiencies make it difficult to meet the needs of refined research on slope stability in complex seasonal freezing environments. There is an urgent need to develop new test equipment and methods to provide more reliable technical support for engineering practice. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the present invention provides a test device and method for indoor simulation of freeze-thaw cycles of seasonally frozen river slopes, which can accurately simulate the freeze-thaw cycle process of seasonally frozen river slopes.

[0007] The present invention provides the following technical solutions:

[0008] In a first aspect, a test device for indoor simulation of freeze-thaw cycles on seasonally frozen river slopes is provided, comprising: a test chamber, an ambient temperature adjustment component, and several data acquisition components;

[0009] The bottom of the test box accommodates a soil layer for simulating a slope and a water body for simulating a river; the environmental temperature adjustment component is arranged on the top of the test box, and the test box is provided with a water inlet pipe and a drain pipe extending into the box;

[0010] Several of the data acquisition components are distributed in the soil layer, the water body, the sample box and / or the test box;

[0011] The bottom of the soil layer extends to below the water body; a waterproof heating element is provided at the interface between the soil layer and the bottom of the water body; the heating element and the ambient temperature adjustment component are adjusted independently of each other; the heating element can start heating during the water freezing stage and the stable freezing stage.

[0012] Optionally, it also includes a control system, which includes a processing module, a first temperature control component and a second temperature control component, the first temperature control component controls the action of the ambient temperature adjustment component; the second temperature control component controls the action of the heating element; the processing module obtains the collected data of the data acquisition component and generates a target adjustment temperature of the second temperature control component; in the water freezing stage and the stable freezing stage, the first temperature control component and the second temperature control component are jointly regulated.

[0013] Optionally, the processing module acquires the collected data of the data collection component and generates a target adjustment temperature of the second temperature control component; in the water freezing stage and the stable freezing stage, the first temperature control component and the second temperature control component are jointly controlled; specifically:

[0014] The first temperature control component adjusts the ambient temperature inside the test chamber according to the set ambient temperature-time change curve;

[0015] According to the current ambient temperature T a , the processing module obtains the freezing thickness h of the water body at the current time t ice and the water level h w (t);

[0016] The processing module calculates the target control temperature T of the heating element when the water body reaches the coexistence of ice layer and liquid layer according to the following formula: b steady ;

[0017]

[0018] Among them, T m is the freezing point temperature, k is the thermal conductivity of water, k b is the thermal conductivity of the ice layer;

[0019] The second temperature control component adjusts the temperature T according to the target of the heating element b steady , heating the bottom of the water body.

[0020] Optionally, the freezing thickness h of the water body can be directly obtained based on the detection data of the ice sensor. ice , or calculate the freezing thickness of the water body h by the following formula ice ;

[0021]

[0022] h w (t)=h0+αt

[0023] Among them, h0 is the base water level height of the water body, α is the rate of change of the water level, c p is the specific heat capacity of water, L is the latent heat, ρ is the density of water, and T0 is the initial temperature of the water body.

[0024] Optionally, the heating element is a graphene heating film, and a waterproof layer is provided on the surface of the graphene heating film.

[0025] Optionally, the data acquisition component includes a temperature sensor, a pore pressure sensor, a normal stress sensor, a laser water level gauge and a tube water level gauge;

[0026] There are several temperature sensors, some of which are set in the test box to detect the ambient temperature, some of which are set at different depths of the water body to detect the water temperature at different depths, and the remaining temperature sensors are set in soil layers at different heights to detect the soil temperature at different heights;

[0027] Pore ​​pressure sensors and normal stress sensors are also provided at different heights of the soil layer;

[0028] The tubular water level gauge is communicated with the drain pipe; the laser water level gauge is arranged on the top of the test box and faces the liquid surface of the water body.

[0029] Optionally, an outlet flow regulating valve is provided on the drain pipe, and the end of the drain pipe facing away from the test box is inserted into the water reservoir. A centrifugal pump is provided inside or outside the water reservoir, and the outlet pipeline of the centrifugal pump is connected to the water inlet pipe, and the water inlet pipe is provided with an inlet flow regulating valve.

[0030] Optionally, the contact surface between the soil layer and the inner wall of the test box is provided with a nanofiber porous ceramic water-permeable filter layer, and the end face of the drainage pipe located inside the test box is also covered with a nanofiber porous ceramic water-permeable filter layer; a soil drainage pipe is provided at the bottom of the soil layer.

[0031] Optionally, the top of the test box can be opened and closed, and the front and back sides are made of light-transmitting and low-temperature-resistant polycarbonate panels; the left and right sides, top and bottom of the test box are provided with insulation layers; the side walls of the test box that are in contact with the soil layer and away from the water body are provided with several sampling grid doors distributed up and down.

[0032] In a second aspect, a test method for indoor simulation of freeze-thaw cycles on seasonally frozen river slopes is provided, and the test device for indoor simulation of freeze-thaw cycles on seasonally frozen river slopes according to any one of the first aspects is provided, comprising:

[0033] Prepare soil samples according to the test purpose and fill them in layers according to the set slope or embed the original soil into the test box;

[0034] The sensors of the data acquisition assembly are placed at various set positions according to the test layout, and heating elements are set at the contact surface between the soil layer and the bottom of the water body;

[0035] Fill the test chamber with water so that the water level is accurately adjusted to the basic water level;

[0036] The freeze-thaw cycle process is simulated as follows: during the freezing stage and the stable freezing stage, the ambient temperature adjustment component cools down or maintains the temperature of the environment inside the test chamber according to the set temperature change curve, and the drain pipe discharges the water inside the test chamber according to the set water level change curve; at the same time, the heating element heats the bottom of the water body, so that the combined effect of the ambient temperature and the temperature of the bottom water body reaches the expected freezing thickness, simulating the stratification scenario of surface freezing and the lower free liquid layer in seasonally frozen rivers; during the thawing stage, the ambient temperature adjustment component heats the environment inside the test chamber according to the set temperature change curve, and the water inlet pipe replenishes the water inside the test chamber according to the set water level change curve;

[0037] Data collection and analysis: During the freeze-thaw cycle, the readings of each sensor are collected and data analysis is performed based on the collected data.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The present invention proposes a test device and method that integrates freeze-thaw bidirectional environmental control, dynamic water level regulation, and multi-parameter real-time monitoring. Through the coordinated regulation of the freeze-thaw bidirectional environmental control system and the water circulation system, combined with a three-dimensional sensor network and intelligent data processing technology, a refined simulation of the freeze-thaw cycle process of seasonally frozen river slopes is achieved. The device can reproduce the natural stratification phenomenon of seasonally frozen river channels with surface freezing and free flow of lower water bodies, support dynamic analysis of soil temperature and stress fields under complex water level change scenarios, and break through the limitations of traditional experiments on independent control of freeze-thaw cycles and water level changes. Through this invention, the evolution law of soil physical and mechanical parameters during the freeze-thaw cycle can be efficiently obtained, providing a scientific basis for the stability assessment of seasonally frozen river slopes, and providing technical support for slope management of water conservancy projects and transportation projects in seasonally frozen areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of the overall structure of the test device for indoor simulation of freeze-thaw cycles of seasonally frozen river slopes of the present invention;

[0041] Figure 2 is a schematic structural diagram of the ambient temperature adjustment assembly of the present invention;

[0042] Figure 3 The present invention is a flow chart of a test method for indoor simulation of freeze-thaw cycles of seasonally frozen river slopes.

[0043] Marked in the figure are: 1 is the test box, 2 is the ambient temperature adjustment component, 3 is the heating element, 4 is the water inlet pipe, 5 is the drain pipe, 6 is the temperature sensor, 7 is the pore pressure sensor, 8 is the normal stress sensor, 9 is the laser water level gauge, 10 is the tubular water level gauge, 11 is the outlet flow regulating valve, 12 is the inlet flow regulating valve, 13 is the water reservoir, 14 is the centrifugal pump, 15 is the permeable filter layer, 16 is the soil drainage pipe, 17 is the sampling grid door, 18 is the exhaust fan, 19 is the air intake grille, 20 is the electromagnetic induction heater, 21 is the compressor, 22 is the condenser, 23 is the evaporator, 24 is the liquid storage tank, 25 is the four-way valve, 26 is the expansion valve, 27 is the regulating valve, 28 is the drying filter, and 29 is the fan. DETAILED DESCRIPTION

[0044] The present invention will now be described in further detail with reference to the accompanying drawings.

[0045] It should be noted that the terms such as "upper", "lower", "left", "right", "front", "back", etc. cited in the invention are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships should be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0046] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the term "comprising" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0047] Example 1

[0048] like Figure 1 As shown, a test device for indoor simulation of freeze-thaw cycles on seasonally frozen river slopes includes: a test box 1, an environmental temperature adjustment component 2 and several data acquisition components.

[0049] The bottom of the test chamber 1 houses a soil layer for simulating a slope and a water body for simulating a river. The top of the test chamber 1 is openable, and the front and back sides are made of light-transmitting, low-temperature-resistant polycarbonate panels. The test chamber 1 has a rectangular, sealed structure and is made of a high-strength, low-thermal-conductivity composite material. The front and back sides of the test chamber 1 are made of high-transmittance, low-temperature-resistant polycarbonate panels for observing the test process. The top is a sliding movable panel, and the bottom is a combination of a pulley bracket and adjustable feet, which facilitates movement while ensuring test stability. The left, right, top, and bottom sides of the test chamber 1 are provided with an insulation layer. The insulation layer can be made of a vacuum insulation panel and aerogel composite insulation material with a thickness of up to 0.15m, effectively isolating it from external environmental interference. The side wall of the test chamber 1 that contacts the soil layer and is away from the water is provided with a number of sampling doors 17 distributed vertically. When the sampling doors 17 are opened, each layer of soil can be sampled.

[0050] The ambient temperature adjustment component 2 is arranged on the top of the test box 1. Specifically, an environmental control box is provided on the top of the test box 1. The environmental control box is provided with an air intake grille 19 and an exhaust fan 18 connected to the atmosphere. The ambient temperature adjustment component 2 is located in the environmental control box, so as to take in and exhaust air into the test box 1; the temperature control range is -40°C to 40°C, with an accuracy of ±0.1°C; the ambient temperature adjustment component 2 can refer to existing technologies, such as air conditioners, integrated cold and hot machines, etc.

[0051] As an alternative, if Figure 2As shown, the ambient temperature adjustment assembly 2 includes a small compressor 21, a condenser 22, an evaporator 23, a liquid storage tank 24, a four-way valve 25, an expansion valve 26, a regulating valve 27, a filter dryer 28, a small fan 29, circulation piping, and an electromagnetic induction heater 20. The compressor 21 compresses the gaseous refrigerant, increasing its pressure and temperature to power the circulation. The condenser 22 cools the high-temperature, high-pressure gaseous refrigerant into a liquid state in cooling mode, releasing heat. During heating, it acts as an evaporator 23 to absorb heat. The evaporator 23 (distributed evaporator 23) absorbs heat during cooling, cooling the air. The low temperature on its surface condenses water vapor in the air, forming condensed water. The four-way valve 25 switches the refrigerant flow direction, enabling switching between cooling and heating modes. The electronic expansion valve 26 precisely regulates the refrigerant flow rate and controls the heat exchange efficiency between the evaporator 23 and condenser 22. The liquid storage tank 24 stores excess liquid refrigerant to balance system pressure fluctuations. Dry filter 28: Removes moisture and impurities from the refrigerant to prevent ice blockage or corrosion. Electromagnetic induction heater 20: Provides auxiliary heating in heating mode, improving heating speed or performance in low-temperature environments. Fan 29: Accelerates air flow and enhances heat exchange between condenser 22 and evaporator 23. Evaporator 23 is equipped with a water collection tank, which collects water condensed on the surface of evaporator 23 to prevent water accumulation. The pipelines of evaporator 23 and condenser 22 are equipped with guide vanes, which guide air evenly through evaporator 23 and condenser 22 to optimize heat exchange. Regulating valve 27: Controls the pressure or flow of the medium (such as water or refrigerant) in the pipeline. Alternatively, an environmentally friendly refrigerant (such as R134a or R290) can be used as the heat transfer medium. Evaporator 23 is equipped with a drain line to remove condensed water generated during the cooling process. When air flows over the low-temperature surface of evaporator 23, the water vapor in the air condenses into liquid water. If the accumulated water is not drained in time, it may cause internal corrosion, mold growth or water leakage of the equipment.

[0052] When the ambient temperature adjustment component 2 is cooling:

[0053] In cooling mode, the compressor 21 compresses the low-temperature, low-pressure gaseous refrigerant into a high-temperature, high-pressure gas and delivers it to the condenser 22. The condenser 22 condenses the gaseous refrigerant into a high-pressure liquid through forced air cooling or water cooling, releasing heat to the external environment. The liquid refrigerant enters the evaporator 23 after being throttled and reduced in pressure by the electronic expansion valve 26. It absorbs heat and vaporizes in a low-pressure environment, lowering the surface temperature of the evaporator 23. When air flows through the evaporator 23, heat is absorbed and the temperature drops. At the same time, the water vapor in the air condenses into liquid condensate on the low-temperature surface, which is collected by the sump and discharged through the drain pipe. The four-way valve 25 maintains the one-way flow of the refrigerant, the liquid storage tank 24 balances the pressure fluctuations of the system, the drying filter 28 absorbs moisture and impurities in the refrigerant, the fan 29 accelerates the air flow to enhance heat exchange, the guide vanes ensure uniform airflow distribution, and the regulating valve 27 accurately controls the refrigerant flow and pressure.

[0054] When the ambient temperature adjustment component 2 is heating:

[0055] The four-way valve 25 switches the refrigerant flow direction, allowing the system to reverse cycle. The high-temperature and high-pressure gaseous refrigerant discharged from the compressor 21 enters the evaporator 23 directly, releasing heat to heat the air, and the refrigerant condenses into a high-pressure liquid. The liquid refrigerant enters the condenser 22 after being reduced in pressure by the electronic expansion valve 26, absorbing ambient heat and vaporizing. If the ambient temperature is lower than the dew point, frost may form on the surface of the condenser 22. The system melts the frost layer through periodic defrosting (short-term switching to cooling mode), and the resulting defrosted water is discharged through the drain pipe. The electromagnetic induction heater 20 assists in improving the heating efficiency in low-temperature environments, the liquid storage tank 24 and the drying filter 28 continue to stabilize the system operation, the fan 29 and the guide vanes optimize the airflow organization, and the regulating valve 27 maintains the refrigerant flow and pressure stability. The condensed water melted from the frost layer is discharged from the evaporator 23 drain pipe during the defrost stage. Its composition is similar to that of the condensed water in the cooling mode, but it may contain more ambient particulate matter.

[0056] The test chamber 1 is provided with an inlet pipe 4 and a drain pipe 5 extending into the chamber; the drain pipe 5 is provided with an outlet flow regulating valve 11. The end of the drain pipe 5 facing away from the test chamber 1 is inserted into a reservoir 13. A centrifugal pump 14 is provided inside or outside the reservoir 13. The outlet pipeline of the centrifugal pump 14 is connected to the inlet pipe 4. The inlet pipe 4 is provided with an inlet flow regulating valve 12. In other words, the inlet pipe 4, the drain pipe 5, the centrifugal pump 14, etc. constitute a water circulation system, thereby simulating the freeze-thaw cycle and reproducing the water level change process of a natural river environment over time. The centrifugal pump 14 is typically a 0-15L / min high-precision variable frequency centrifugal pump 14, and the reservoir 13 is a large-capacity insulated reservoir 13. The inlet flow regulating valve 12 and the outlet flow regulating valve 11 can use intelligent flow regulating valves 27 such as electronically controlled valves to control the water level accuracy to ±0.02m.

[0057] Furthermore, a soil drainage pipe 16 is provided at the bottom of the soil layer. To prevent soil particles from entering the water circulation system and causing soil loss while ensuring normal water infiltration, a nanofiber porous ceramic water-permeable filter layer 15 is provided at the interface between the soil layer and the inner wall of the test chamber 1. The end face of the drainage pipe 5 located inside the test chamber 1 is covered with the nanofiber porous ceramic water-permeable filter layer 15; the nanofiber porous ceramic water-permeable filter layer 15 can refer to the existing technology.

[0058] Several of the data acquisition components are distributed in the soil layer, the water body, the sample box and / or the outside of the test box 1; the data acquisition components include a temperature sensor 6, a pore pressure sensor 7, a normal stress sensor 8, a laser water level meter 9 and a tube water level meter 10; there are several temperature sensors 6, some of which are arranged in the test box 1 to detect the ambient temperature, another part of the temperature sensors 6 are arranged at different depths of the water body to detect the water temperature at different depths, and the remaining temperature sensors 6 are arranged in the soil layer at different heights to detect the soil temperature at different heights; the temperature sensor 6 is a high-sensitivity temperature sensor based on MEMS (microelectromechanical system) and nanomaterials (quantum tunneling thermistor, accuracy 0.01°C, temperature range of -60°C-80°C), and pore pressure sensors 7 and normal stress sensors 8 are also arranged at different heights of the soil layer; the pore pressure sensor 7 is an integrated nanopiezoresistive chip with an accuracy of ±0.1kPa, and the normal stress sensor 8 is a flexible capacitor array. Of course, in some other embodiments, displacement sensors are also provided, which are arranged on the slope surface and shallow layer to monitor soil deformation. A tubular water level gauge 10 is connected to the drainage pipe 5; and a laser water level gauge 9 is provided on the top of the test box 1.

[0059] The bottom of the soil layer extends below the water body; the interface between the soil layer and the bottom of the water body is equipped with a waterproof heating element 3. Heating element 3 is a graphene heating film with a waterproof layer on its surface. Of course, heating element 3 can also use graphene heating film and flexible circuit board integration technology, and the temperature gradient can be precisely set within the range of -5°C to 10°C according to test requirements. Heating element 3 and ambient temperature adjustment component 2 are adjusted independently of each other; during the freezing and stable freezing stages of the water body, heating element 3 can start heating. Heating element 3 and ambient temperature adjustment component 2 work together to simulate the vertical stratification of natural water temperature, providing precise control conditions for studying the impact of the water temperature field on the freeze-thaw process of slope soil.

[0060] Furthermore, a test device for indoor simulation of freeze-thaw cycles on seasonally frozen river slopes also includes a control system, comprising a processing module, a first temperature control component, and a second temperature control component. The first temperature control component controls the operation of the ambient temperature adjustment component 2; the second temperature control component controls the operation of the heater 3. The processing module acquires data from the data acquisition component and generates a target adjustment temperature for the second temperature control component. During the freezing and stable freezing stages of the water body, the first and second temperature control components jointly regulate the temperature; during the thawing stage, the first temperature control component independently regulates the ambient temperature. A temperature control display can be provided on the test chamber 1 to display the ambient temperature or the heating temperature of the heater 3.

[0061] The processing module obtains the collected data of the data acquisition component and generates the target adjustment temperature of the second temperature control component; in the water freezing stage and the stable freezing stage, the first temperature control component and the second temperature control component jointly control, specifically: the first temperature control component adjusts the ambient temperature in the test box 1 according to the set ambient temperature-time change curve; according to the current ambient temperature T a , the processing module obtains the freezing thickness h of the water body at the current time t ice and the water level h w (t); The processing module calculates the target control temperature T of the heating element 3 when the water body reaches the coexistence of ice layer and liquid layer according to the following formula b steady The second temperature control component controls the temperature T according to the target of the heating element 3 b steady , heating the bottom of the water body.

[0062]

[0063] Among them, T m is the freezing point temperature, k is the thermal conductivity of water, k b is the thermal conductivity of the ice layer.

[0064] Among them, the freezing thickness of the water body h ice The frozen thickness h of the water body can be directly obtained based on the detection data of the set ice sensor ice , or calculate the freezing thickness of the water body h by the following formula ice ;

[0065]

[0066] h w (t)=h0+αt

[0067] Among them, h0 is the base water level height of the water body, α is the rate of change of the water level, c pis the specific heat capacity of water, L is the latent heat, ρ is the density of water, and T0 is the initial temperature of the water body.

[0068] Through the above method, the heating element 3 and the ambient temperature adjustment component 2 can act simultaneously, thereby more accurately simulating the real stratification scene of the surface water freezing and the lower free liquid layer during the freeze-thaw cycle of the natural seasonally frozen river slope soil.

[0069] Example 2

[0070] like Figure 3 As shown, a test method for indoor simulation of freeze-thaw cycles on seasonally frozen river slopes includes the following steps:

[0071] S1: Prepare soil samples according to the test purpose, and fill the soil samples in layers according to the set slope or implant the original soil into the test box 1.

[0072] Specifically, soils such as clay and silt are selected based on the test objectives, and their initial physical properties, such as moisture content, density, and particle size distribution, are measured. The test area is adjusted according to the designed slope, supporting both layered filling and undisturbed soil placement. Layered filling is performed with a thickness of 0.1-0.3m per layer, with permeable geotextiles laid between layers. Alternatively, the prototype soil can be placed in a removable prefabricated mold within the test area. The number of soil sample layers, their thickness, and the sensor layout can be flexibly adjusted based on research needs.

[0073] S2: Place the sensors of the data acquisition assembly at respective set positions according to the test layout, and set a heating element 3 on the contact surface between the soil layer and the bottom of the water body.

[0074] Temperature sensors 6 are arranged in a three-dimensional grid to monitor temperature changes at various locations within the soil. Pore pressure sensors 7 are placed near potential sliding surfaces to monitor pore water pressure changes. Displacement sensors are placed on the slope surface and in shallow layers to monitor soil deformation. Pressure sensors are embedded in each soil layer to monitor normal stress. This strategic sensor layout enables comprehensive and accurate acquisition of test data, providing a reliable basis for subsequent analysis. Sensor data is transmitted via a high-speed, low-noise fiber-optic data network to an intelligent data acquisition terminal. This terminal incorporates a high-performance microprocessor and a large cache, ensuring stable and reliable data transmission to the computer control system for in-depth analysis and processing.

[0075] S3: Fill the test chamber 1 with water so that the water level is accurately adjusted to the basic water level.

[0076] The centrifugal pump 14 is started to allow water to enter the sample box.

[0077] S4: Simulate the freeze-thaw cycle process, specifically: in the freezing stage and the stable freezing stage, according to the set temperature change curve, the ambient temperature adjustment component 2 cools down or maintains the temperature of the environment in the test box 1, and according to the set water level change curve, the drain pipe 5 discharges the water in the test box 1; at the same time, the heating element 3 heats the bottom of the water body, so that the combined effect of the ambient temperature and the bottom water temperature can achieve the expected freezing thickness, simulating the stratification scene of surface freezing and the lower free liquid layer in seasonally frozen rivers; in the melting stage, according to the set temperature change curve, the ambient temperature adjustment component 2 heats the environment in the test box 1, and according to the set water level change curve, the water inlet pipe 4 replenishes the water in the test box 1.

[0078] Specifically, the freezing process requires the removal of two types of heat: sensible heat: cooling the water from T0 to T m , the heat is ρc p (T0-T m )h ice (The initial water temperature T0 is the preset temperature of the bottom heating plate); Latent heat: the heat released when water freezes, which is ρLh ice .

[0079] The heat flux through the ice layer is 2k(T m -T a ) / h ice , duration is t, total heat conducted is 2k(T m -T a )t / h ice .

[0080] The heat conducted is equal to the total heat to be removed:

[0081]

[0082] The solution is:

[0083]

[0084] Assume h w (t) The change is known, such as linear growth: h w (t) = h0 + αt, by defining the equivalent freezing time:

[0085]

[0086] At this time, the freezing depth formula becomes:

[0087]

[0088] By defining t' as the "equivalent freezing time," the impact of the dynamic water level is converted into a correction to time t. The core idea is that when the water level is high, more heat needs to be removed per unit time, which effectively "slows" the freezing rate. Therefore, t' can be understood as the "effective freezing time after accounting for water level changes."

[0089] It is worth noting that when the dynamic change rate of the water level is small, the equivalent freezing time t' is approximately equal to the set time t, so the set freezing / thawing time can be slightly extended during the test.

[0090] When the ice layer grows to a certain extent, the bottom heating plate is turned on. When the heat provided by the heating plate and the heat lost through the ice layer reach a balance, the ice layer stops growing and the liquid layer remains stable. In this case, the ice layer thickness and the bottom heating plate temperature T in the steady state can be solved. b The relationship between T b control effect.

[0091] Heat flux density of ice layer heat conduction:

[0092]

[0093] The bottom heating plate inputs heat flux density to the liquid water layer:

[0094]

[0095] At the ice-water interface, the heat conduction must balance the rate of latent heat release due to phase change:

[0096]

[0097] Combining the above equations, we can get the ice growth rate:

[0098]

[0099] when When q top =q bottom Right now:

[0100]

[0101] When T b <T b steady When T b =T m When , it degenerates into the situation without heating plate and the water body is completely frozen.

[0102] When T b >T bsteady When T b >>T m When , the liquid layer occupies the entire water depth.

[0103] The bottom heating plate temperature T is determined by the dynamic balance between heat conduction and heating input. b It plays a key role in suppressing complete freezing, controlling the thickness of the ice layer and the ratio of the liquid layer, and maintaining water stratification.

[0104] Freeze period, v = dT / dt = αe βt (℃ / h) rate according to the exponential curve to the specified temperature, and continue for a specified time; the stable freezing period, keep at the specified temperature and continue for a specific time; the melting period, v = dT / dt = α (1-e βt The temperature is raised exponentially at a rate of )(℃ / h) to the specified temperature and maintained for a certain period of time; the temperature and duration of the freezing period, stable period and melting period are determined according to the test purpose.

[0105] During the freeze-thaw cycle, the water circulation system accurately adjusts the initial water level to the reference water level h0. The water level-time curve h~t is set based on complex water level processes such as rapid water rise during the thawing period and slow water fall during the freezing period.

[0106] During the freeze-thaw cycle, the air flow distribution system optimizes the fan speed and guide blade angle through computational fluid dynamics, so that the air in the box forms a stable and uniform temperature laminar flow, avoiding local temperature gradients and air flow vortices, and ensuring that the heating or cooling rate of various parts of the soil is consistent.

[0107] During the freeze-thaw cycle, after each freeze-thaw cycle is completed, a sampling period is set for soil sample collection and environmental restoration. The specific operations are as follows: turn off the temperature control module of the refrigeration / heating system, suspend the freeze-thaw cycle program, and keep the waterproof heating element 3 at the bottom of the water body running at low power (maintaining temperature fluctuations ≤±0.2°C) to reduce temperature disturbances in the box. Open the sampling grid on the side of the test box, and use a micro-soil sampler to extract soil samples in layers along the preset sampling channel. Sampling avoids the sensor area, and focuses on collecting soil at potential sliding surfaces and freeze-thaw interfaces. Sample 3 points in each layer, and immediately seal them in an insulated container after sampling to ensure that the physical state of the soil sample is consistent with the test conditions. After sampling is completed, close the sampling grid and restart the environmental control system. Perform rapid temperature compensation for 0.5-2h according to the preset temperature curve, monitor the temperature uniformity in the box through the temperature sensor 6, and start the next freeze-thaw cycle after confirming that it has returned to the target test conditions.

[0108] S5: Data Acquisition and Analysis: During the freeze-thaw cycle, the readings of various sensors are collected and analyzed. Temperature, pore water pressure, normal stress, and displacement data are recorded in real time to monitor changes during the freeze-thaw process. The acquisition frequency is determined based on the specific experimental conditions, with a higher frequency during the freeze / thaw phase than during the stable phase. Data is transmitted to a computer system in real time for storage, and a dynamic curve of parameter changes during the freeze-thaw cycle is generated.

[0109] Table 1 Sensors and measurement parameters

[0110] Measurement parameters Sensor Type Data usage <![CDATA[Temperature T a , T0]]> Temperature sensor Calculate freezing depth and temperature gradient Pore ​​water pressure u Pore ​​pressure sensor Calculation of effective stress and anti-slip force Normal stress σ pressure sensor Calculate anti-slip force Slope displacement Δ Displacement Sensor Verify slope instability trend Water level h Laser water level meter Measuring water levels

[0111] Data analysis can be determined according to the purpose of the experiment. Usually, the following data analysis content can be used:

[0112] 1. Pore water pressure analysis: In the experiment, the effect of water level changes on pore water pressure was particularly significant. As the freeze-thaw cycle progressed, the rise and fall of the water level caused fluctuations in pore water pressure. Especially during the freezing process, when the frozen layer of water body formed, the pore water pressure increased; while during the thawing stage, the change of water level caused rapid changes in pore water pressure. By correlating and analyzing the effect of water level fluctuation on pore water pressure around the sliding surface, the pore water pressure u under different water level and temperature conditions was determined. The data was used to calculate the effective stress:

[0113] σ′=σ-u

[0114] Among them, σ' is the effective stress; σ is the total stress; and u is the pore water pressure.

[0115] 2. Soil strength analysis: Calculate the effect of freeze-thaw cycles on soil strength using the stress and moisture content measured in the test:

[0116] C f =C0·exp(-β·n)

[0117] Among them, C f is the shear strength of the soil after freezing and thawing; C0 is the initial shear strength of the soil; β is the attenuation coefficient of the freeze-thaw cycle; and n is the number of freeze-thaw cycles.

[0118] 3. Slope stability analysis: Based on multiple data collected by sensors, the slope stability coefficient F is calculated using the limit equilibrium method or finite element method. s : Slope stability coefficient F s It is a key indicator for measuring slope stability. s >1 when the slope is stable, F s When <1, the slope may become unstable, and its calculation involves the anti-sliding force and sliding force in the slope soil.

[0119]

[0120] The anti-sliding force R mainly comes from the shear strength of the soil, which is calculated using the Mohr-Coulomb strength theory:

[0121]

[0122] Combined with the c, σ, u and Calculate the anti-slip force R.

[0123] The sliding force S comes from the component of the slope force along the sliding surface under the action of gravity. The sliding force S is calculated based on the slope gravity formula combined with the soil density ρ, volume V and slope angle α.

[0124] S=W·sinα

[0125] Where c is the cohesion of the soil (i.e. the shear strength C f , obtained by measuring the shear mechanical properties of the soil using the test device); A is the area on the potential sliding surface (determined according to the slope geometry of the test device); σ' is the effective stress (calculated by pore water pressure analysis, i.e., σ-u); σ is the normal stress (measured by the pressure sensor); u is the pore water pressure (measured by the pore pressure sensor 7); is the internal friction angle of the soil (which can be obtained by measuring the shear mechanical properties of the soil through the test device); W is the gravity of the soil (which can be calculated based on the density and volume of the test soil); α is the slope angle (the slope angle can be adjusted by the test device).

[0126] Comparison of pore water pressure u, normal stress σ, displacement Δ and slope stability coefficient F under different freeze-thaw cycle numbers n and environmental conditions (such as temperature range T, duration t, etc.) s Value, plot water level h, temperature and stability coefficient F s The relationship curve of the freezing and thawing cycles of seasonally frozen rivers was analyzed to analyze its changing pattern and evaluate the impact of the freezing and thawing cycles of seasonally frozen rivers on slope stability.

[0127] 4. Correlation analysis: Based on the random forest algorithm (Python), the effect of multiple parameters (ambient temperature T, freeze-thaw times n, slope i, water level h, etc.) on the stability coefficient (F s ) is the weighted contribution. Based on the relevant data of freeze-thaw cycle simulation of seasonally frozen river slopes measured in the above steps, missing values ​​and outliers are processed, and then the training set and test set are divided into 80%-20% ratios for model training. The Random Forest Regressor in the Scikit-earn library is selected, and hyperparameters such as the number of decision trees, maximum depth, and minimum number of samples for node splitting are set. The model is evaluated and tuned, and the trained model is used to predict the test set. The mean square error (MSE), root mean square error (RMSE), and coefficient of determination (R2 ) and other indicators, using grid search combined with cross-validation to find the optimal hyperparameter combination. A random forest model was used to derive scores for each feature and visualize them in the form of bar charts.

[0128] Example 3

[0129] This paper provides a simulation of the freeze-thaw cycle process of the river slope in the lower reaches of the Songhua River. Through data research and field observation, the specific layout of the freeze-thaw cycle indoor simulation test device is introduced.

[0130] The internal space of the test chamber is divided into an environmental control area and a soil test area. The environmental control area is located at the top of the chamber and contains a temperature control cabin and an intelligent controller, as well as an external power supply, for regulating the test environment.

[0131] The test apparatus utilizes high-strength, low-thermal-conductivity composite materials to construct a sealed enclosure measuring 3.0m x 1.8m x 2.5m. The front and back sides are lined with 0.1m-thick, low-temperature-resistant polycarbonate panels with a light transmittance exceeding 92%. The side walls, top, and bottom of the enclosure are insulated with a 0.15m-thick vacuum insulation panel and aerogel composite layer with a thermal conductivity of ≤0.008W / (m·K), effectively isolating the enclosure from external interference. Adjustable feet and a pulley system at the bottom ensure both stability and ease of movement.

[0132] The interior is divided into an environmental control area and a soil test area. The soil test area is located in the lower part of the box, with a size of 1.2m×1.8m×1m. It is equipped with a 4-layer soil structure, each layer is 0.2m thick, and a permeable geotextile (permeability coefficient 1×10 - 3 cm / s), surrounded by a nanofiber porous ceramic filter layer with a porosity of ≥60%.

[0133] The top environmental control chamber measures 1.5m x 1.8m x 0.6m and features a built-in computational fluid dynamics-optimized air duct system to ensure uniform airflow across the soil surface. It utilizes a two-stage compression variable-frequency refrigeration unit equipped with R134a, an environmentally friendly refrigerant, with a temperature control range of -40°C to 40°C, with an accuracy of ±0.1°C. The refrigeration system utilizes a four-way valve to switch between heating and cooling, supplemented by an electromagnetic induction heater to ensure accurate reproduction of the temperature curve.

[0134] A 0.08m thick graphene waterproof heating plate is installed at the bottom of the water body, with a power density of 0-200W / m 2 , supports gradient temperature control from -5℃ to 10℃, and can realize stratified freezing control of water bodies.

[0135] The water circulation system is driven by a high-precision centrifugal pump (0-15 L / min) and equipped with a laser water level gauge to achieve ±0.02 m water level accuracy. 50 mm x 5 mm PEX-AL-PEX composite piping is connected to an intelligent flow control valve, which dynamically adjusts water flow rate and flow distribution according to a preset curve. The insulated water reservoir has a capacity sufficient for 300 hours of continuous circulation, with the zero water level reference set above the heating plate.

[0136] The data acquisition system consists of high-sensitivity temperature (quantum tunneling thermistor, accuracy of 0.01°C, temperature range of -60°C-80°C), pore water pressure (nano-piezoresistive chip integration, accuracy of ±0.1kPa), normal stress (flexible capacitor array) and displacement (laser interferometer-fiber Bragg grating hybrid) sensors based on MEMS (micro-electromechanical systems) and nanomaterials, as well as an optical fiber data transmission network and an intelligent data acquisition terminal.

[0137] The computer control system uses high-performance industrial computers and software, and Ethernet connects various systems.

[0138] The specific steps of the freeze-thaw cycle indoor simulation test method are as follows:

[0139] Step 1: The test soil is clay with a water content of 18% and a dry density of 1.6 g / cm 3 The total thickness of the test soil should be set according to the size of the test area and the purpose of the test. In this test device, the range is 0-1.5m. In this case, the total thickness of the test soil is set to h s =1m. Based on the actual freeze-thaw impact depth and simulation requirements, the number of test soil layers (m) was set to 5, with a 0.2m interval between each layer. The slope gradient of the simulated seasonally frozen river soil was set to i = 45°, consistent with the actual river slope gradient, to ensure that the test fully reflects changes in slope stability.

[0140] Step 2: Sensor layout. The sensors in this case are arranged in the following way:

[0141] Temperature sensors: They are arranged in a three-dimensional grid with a vertical spacing of 0.2m and a horizontal spacing of 0.3m inside each soil layer to record the temperature changes of each soil layer; at the same time, 20 temperature sensors are installed at equal intervals in different positions in the test chamber environment to monitor the ambient temperature T a Changes in ambient temperature T a Vertical distribution T in the test chamber space ai , (i is the layout layer of the ambient temperature sensor); 5 temperature sensors are arranged vertically in the water body to monitor the changes in the water temperature T0.

[0142] Pore ​​pressure sensors: These are placed on the potential sliding surface and in the upper middle of the soil to monitor changes in pore water pressure u during freeze-thaw cycles. Four sensors are placed on each layer, two at 0.05 m from the top of the soil layer, and two at 0.05 m from the bottom, for a total of 20 sensors.

[0143] Pressure sensors: arranged on the potential sliding surface of the soil to monitor the normal stress σ and its distribution during the freeze-thaw process. Two sensors are arranged on each layer, for a total of 10 sensors.

[0144] Displacement sensors: Three displacement sensors were placed vertically along the slope surface, one at the top, one in the middle (0.4m and 0.8m from the top), and one at the bottom (0.2m from the bottom). These sensors monitored the overall displacement change Δ of the slope. Two additional displacement sensors were placed at potential sliding surfaces (estimated based on experience or previous tests) to focus on monitoring soil displacement at these surfaces. Furthermore, a displacement sensor was placed within each layer of the soil, located at the center of that layer, to monitor internal deformation. A total of ten displacement sensors were used.

[0145] Each sensor is connected to the data acquisition system via cables, ensuring real-time data transmission to the computer control module for analysis. The water circulation system's pipes are connected to the water level gauge and pump system to ensure precise control of water level fluctuations. Furthermore, the waterproof heating plate's connection to the power supply and temperature control system is checked to ensure proper function and accurate regulation of the water bottom temperature according to the computer control module's instructions.

[0146] Step 3: Simulate freeze-thaw cycles. First, set the freeze-thaw cycle temperature range to -30℃-20℃ according to climate data and test purpose, and set the diurnal or seasonal change cycle and rate: the freezing period is v=dT / dt=-0.5e -0.1t (℃ / h) nonlinear cooling (from 20℃ to -30℃, lasting 72h), simulating the cooling process in autumn and winter; stable freezing period, maintaining -30℃±2℃ for 120h; melting period according to v=dT / dt=1.2(1-e -0.2t )(℃ / h) accelerated temperature rise (from -30℃ to 10℃, lasting 48h), in line with the law of increased sunshine in spring.

[0147] The number of freeze-thaw cycles n in this case is set to 5 times, and each freeze-thaw cycle lasts 240 h.

[0148] In this case study, the initial water level was set at 0.6 m from the soil bottom. The water level curve h to t was developed based on the complex water level processes of seasonally frozen rivers, such as rapid water rise during the thaw period and slow water fall during the freezing period. Due to the seasonal characteristics of seasonally frozen rivers, the water level gradually rises during the spring thaw and falls during the winter freeze period. During the freezing period, the water level dropped at a rate of 0.01 m / h for approximately 40 hours, decreasing from 0.6 m to 0.2 m and maintaining this level until the thaw period. During the thaw period, the water level then rose at a rate of 0.02 m / h for approximately 20 hours, rising from 0.2 to 0.6 m. During the experiment, water level fluctuations were controlled using a laser water level gauge and inlet and outlet flow control valves to further investigate the impact of water level fluctuations on the slope stability of seasonally frozen rivers.

[0149] The intelligent controller activates the refrigeration system. The variable-frequency compressor in the environmental control box evenly introduces cold air into the test chamber. The cool air is diffused through guide vanes, fans, and airflow grilles, ensuring uniform cooling and preventing rapid freezing of soil areas that could cause cracks. The intelligent controller dynamically adjusts cooling power based on feedback from the temperature sensor, maintaining a smooth cooling curve and recording the expansion of the frozen layer.

[0150] During the cooling process, the bottom temperature of the water body is monitored in real time. When the surface temperature of the water body approaches the freezing point, the intelligent controller controls the power of the bottom waterproof heating plate to maintain the bottom temperature of the water body at 0-1°C, forming a water temperature gradient, so that the ambient temperature and the bottom water temperature work together to achieve the expected freezing thickness h ice , simulating the natural stratification state in the natural environment where the surface of the water body is frozen and the lower layer is still free water.

[0151] The temperature was lowered for 72 hours according to the set cooling curve. After the cooling was completed, it entered a stable freezing period of -30℃, which lasted for 120 hours.

[0152] During the temperature rise process, the intelligent controller activates the heating device. A four-way valve redirects the refrigerant flow in the refrigeration cycle to achieve a heating effect. A parallel electromagnetic induction heater then provides additional heat. Airflow grilles evenly distribute the hot air to prevent local overheating. Feedback from the temperature sensor dynamically adjusts the intelligent controller to maintain a smooth temperature rise curve and record the reduction in the frozen layer thickness.

[0153] During the heating process, the temperature change curves of each soil layer are recorded in real time, the temperature at the bottom of the water body is monitored, and the power of the waterproof heating plate is adjusted according to the preset temperature control strategy through the computer control module, so that the temperature at the bottom of the water body rises steadily and changes in coordination with the soil and ambient temperature.

[0154] During the freeze-thaw cycle, the opening of the intelligent flow inlet and outlet flow regulating valves is dynamically adjusted according to the set temperature-water level-time change curve, and precise distribution of water level and flow is achieved through electromagnetic drive.

[0155] During the freeze-thaw cycle, the air flow distribution system optimizes the fan speed and guide blade angle through computational fluid dynamics, so that the air in the box forms a stable and uniform temperature laminar flow, avoiding local temperature gradients and air flow vortices, and ensuring that the heating or cooling rate of various parts of the soil is consistent.

[0156] During the freeze-thaw cycle, a sampling period is set up after each freeze-thaw cycle (in this case, sampling is done after the first, third, and fifth freeze-thaw cycles) to collect soil samples and restore the environment. The specific operations are as follows:

[0157] Turn off the main control module of the refrigeration / heating system, suspend the freeze-thaw cycle program, keep the waterproof heating plate at the bottom of the water body running at low power (maintain temperature fluctuation ≤±0.2℃) to reduce temperature disturbances in the box. Open the sampling grid on the side of the test box, use a micro-soil sampler to extract soil samples in layers along the preset sampling channel, avoid the sensor area during sampling, and focus on collecting soil at potential sliding surfaces and freeze-thaw interfaces. The sampling volume is 50g each time. Sampling is performed at 3 points in each layer to ensure the representativeness and comprehensiveness of the data. Immediately after sampling, seal it in an insulated container to ensure that the physical state of the soil sample is consistent with the test conditions.

[0158] The soil sample testing and analysis after sampling include: in terms of soil mechanical parameters, the shear strength, cohesion and internal friction angle of the soil are measured through triaxial shear tests, the influence of freeze-thaw cycles on soil strength is analyzed, and compression tests are carried out to detect the compression modulus and consolidation changes of the soil; in terms of permeability parameters, the influence of freeze-thaw cycles on soil permeability is evaluated by permeability tests, and the water migration law and its influence on pore water pressure are analyzed; in terms of physical and chemical properties, the changes in soil moisture content, porosity and particle structure are analyzed, and the refinement of soil particles and the expansion of internal cracks after freeze-thaw cycles are detected.

[0159] After sampling is completed, close the sampling grid and restart the environmental control system. Perform rapid temperature compensation for 1 hour according to the preset temperature curve. Monitor the temperature uniformity in the box through the temperature sensor, confirm that it has returned to 20°C, and start the next freeze-thaw cycle.

[0160] Step 4: Data collection and recording.

[0161] Observation and recording of test phenomena: possible local cracks or damage in the soil; temperature changes at the freeze-thaw interface; temperature differences between the surface and deep layers of the soil-water body; dynamic changes in pore water pressure in each soil layer and water migration during freeze-thaw, especially pressure fluctuations near the sliding surface. Test data collection frequency is twice per hour during the freeze / thaw phase and once every two hours during the stabilization phase.

[0162] Temperature data: Temperature curves for each soil layer and slope surface; the position of frozen and thawed layers changes dynamically over time. Temperature sensors placed at various locations capture detailed temperature data, including temperature variations at different depths within the soil, on the slope surface, and at different depths in water bodies, to analyze the distribution and evolution of the temperature field.

[0163] Pore-water pressure data: Monitor pore-water pressure fluctuations, particularly those during the early stages of freezing and thawing. Record pore-water pressure changes near the sliding surface and analyze their impact on slope stability. Using data from pore-pressure sensors, investigate how water level changes and freeze-thaw cycles affect pore-water pressure, and the relationship between pore-water pressure and slope instability.

[0164] Soil displacement data: Records displacement curves of the slope surface, focusing on potential sliding surfaces, for analysis of sliding trends and soil deformation patterns. Data from displacement sensors can be used to assess slope stability during freeze-thaw cycles and predict potential instability.

[0165] Water level fluctuation data: Record water level-time curves to analyze the impact of water level fluctuations on pore water pressure. Simulate the effects of rising water levels during the spring thaw and falling water levels during the winter dry season on slope stability. Combined with water level gauge data, investigate the relationship between water level fluctuations and other parameters (such as pore water pressure and soil strength), as well as the role of water level fluctuations in slope stability.

[0166] Data storage and transmission: All data is transmitted to the computer control module in real time through the data acquisition system and stored as standardized test record files for subsequent analysis and visualization. This ensures the stability and accuracy of data transmission and avoids data loss or errors.

[0167] Step 5:

[0168] Conduct freezing depth analysis, pore water pressure analysis, soil strength analysis, and slope stability analysis, generate freeze-thaw cycle curves and data visualization charts, evaluate slope stability, verify the stability of test results, study the effects of different conditions (such as freeze-thaw rate, water level fluctuation, soil slope, etc.) on slope stability, and analyze parameter correlation.

[0169] 1. Pore water pressure analysis: In the experiment, the effect of water level changes on pore water pressure was particularly significant. As the freeze-thaw cycle progressed, the rise and fall of the water level caused fluctuations in pore water pressure. Especially during the freezing process, when the frozen layer of water body formed, the pore water pressure increased; while during the thawing stage, the change of water level caused rapid changes in pore water pressure. By correlating and analyzing the effect of water level fluctuation on pore water pressure around the sliding surface, the pore water pressure u under different water level and temperature conditions was determined. The data was used to calculate the effective stress:

[0170] σ′=σ-u

[0171] Among them, σ' is the effective stress; σ is the total stress; and u is the pore water pressure.

[0172] 2. Soil strength analysis: Calculate the effect of freeze-thaw cycles on soil strength using the stress and moisture content data measured in the test:

[0173] C f =C0·exp(-β·n)

[0174] Among them, C f is the shear strength of the soil after freezing and thawing; C0 is the initial shear strength of the soil; β is the attenuation coefficient of the freeze-thaw cycle; and n is the number of freeze-thaw cycles.

[0175] 3. Slope stability analysis: Based on the test data, calculate the slope stability coefficient F using the limit equilibrium method or finite element method s : Slope stability coefficient F s It is a key indicator for measuring slope stability. s >1 when the slope is stable, F s When <1, the slope may become unstable, and its calculation involves the anti-sliding force and sliding force in the slope soil.

[0176]

[0177] The anti-sliding force R mainly comes from the shear strength of the soil, which is calculated using the Mohr-Coulomb strength theory:

[0178]

[0179] Combined with the c, σ, u and Calculate the anti-slip force R.

[0180] The sliding force S comes from the component of the slope force along the sliding surface under the action of gravity. The sliding force S is calculated based on the slope gravity formula combined with the soil density ρ, volume V and slope angle α.

[0181] S=W·sinα

[0182] Where c is the cohesion of the soil (i.e. the shear strength C f , obtained by measuring the shear mechanical properties of the soil using a test device); A is the area on the potential sliding surface (determined based on the slope geometry of the test device); σ' is the effective stress (calculated by pore water pressure analysis, i.e., σ-u); σ is the normal stress (measured by a pressure sensor); and u is the pore water pressure (measured by a pore pressure sensor). is the internal friction angle of the soil (which can be obtained by measuring the shear mechanical properties of the soil through the test device); W is the gravity of the soil (which can be calculated based on the density and volume of the test soil); α is the slope angle (the slope angle can be adjusted by the test device).

[0183] Comparison of pore water pressure u, normal stress σ, displacement Δ and slope stability coefficient F under different freeze-thaw cycle numbers n and environmental conditions (such as temperature range T, duration t, etc.) s Value, plot water level h, temperature and stability coefficient F s The relationship curve of the freezing and thawing cycles of seasonally frozen rivers was analyzed to analyze its changing pattern and evaluate the impact of the freezing and thawing cycles of seasonally frozen rivers on slope stability.

[0184] 4. Correlation analysis: Based on the random forest algorithm (Python), the effect of multiple parameters (ambient temperature T, freeze-thaw times n, slope i, water level h, etc.) on the stability coefficient (F s ) is the weighted contribution. Based on the relevant data of freeze-thaw cycle simulation of seasonally frozen river slopes measured in the above steps, missing values ​​and outliers are processed, and then the training set and test set are divided into 80%-20% ratios for model training. The Random Forest Regressor in the Scikit-earn library is selected, and hyperparameters such as the number of decision trees, maximum depth, and minimum number of samples for node splitting are set. The model is evaluated and tuned, and the trained model is used to predict the test set. The mean square error (MSE), root mean square error (RMSE), and coefficient of determination (R 2 ) and other indicators, using grid search combined with cross-validation to find the optimal hyperparameter combination. A random forest model was used to derive scores for each feature and visualize them in the form of bar charts.

[0185] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0186] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A test device for indoor simulation of freeze-thaw cycles on seasonally frozen river slopes, characterized in that: include: A test chamber (1), an environmental temperature adjustment component (2), and several data acquisition components; The bottom of the test box (1) accommodates a soil layer for simulating a slope and a water body for simulating a river; the environmental temperature adjustment component (2) is arranged on the top of the test box (1); and the test box (1) is provided with a water inlet pipe (4) and a drain pipe (5) extending into the box; Several of the data acquisition components are distributed in the soil layer, the water body, the sample box and / or the outside of the test box (1); The bottom of the soil layer extends to below the water body; a waterproof heating element (3) is provided at the interface where the soil layer contacts the bottom of the water body; the heating element (3) and the ambient temperature adjustment component (2) are adjusted independently of each other; and the heating element (3) can start heating during the freezing stage and the stable freezing stage of the water body.

2. The test device for indoor simulation of freeze-thaw cycles of seasonally frozen river slopes according to claim 1 is characterized in that: The invention also includes a control system, which includes a processing module, a first temperature control component and a second temperature control component, wherein the first temperature control component controls the action of the ambient temperature adjustment component (2); the second temperature control component controls the action of the heating element (3); the processing module obtains the collected data of the data collection component and generates a target adjustment temperature of the second temperature control component; in the water body freezing stage and the stable freezing stage, the first temperature control component and the second temperature control component are jointly controlled.

3. The test device for indoor simulation of freeze-thaw cycles of seasonally frozen river slopes according to claim 2, characterized in that: The processing module acquires the collected data of the data collection component and generates a target adjustment temperature of the second temperature control component; in the water freezing stage and the stable freezing stage, the first temperature control component and the second temperature control component are jointly controlled; specifically: The first temperature control component adjusts the ambient temperature in the test box (1) according to a set ambient temperature-time variation curve; According to the current ambient temperature T a , the processing module obtains the freezing thickness h of the water body at the current time t ice and the water level h w (t); The processing module calculates the target control temperature T of the heating element (3) when the water body reaches the coexistence of ice layer and liquid layer according to the following formula: b steady ; Among them, T m is the freezing point temperature, k is the thermal conductivity of water, k b is the thermal conductivity of the ice layer; The second temperature control component adjusts the temperature T according to the target of the heating element (3) b steady , heating the bottom of the water body.

4. The test device for indoor simulation of freeze-thaw cycles of seasonally frozen river slopes according to claim 3, characterized in that: According to the detection data of the ice sensor, the freezing thickness h of the water body is directly obtained ice , or calculate the freezing thickness of the water body h by the following formula ice ; h w (t)=h0+αt Among them, h0 is the base water level height of the water body, α is the rate of change of the water level, c p is the specific heat capacity of water, L is the latent heat, ρ is the density of water, and T0 is the initial temperature of the water body.

5. The test device for indoor simulation of freeze-thaw cycles of seasonally frozen river slopes according to claim 1, characterized in that: The heating element (3) is a graphene heating film, and a waterproof layer is provided on the surface of the graphene heating film.

6. The test device for indoor simulation of freeze-thaw cycles of seasonally frozen river slopes according to claim 1, characterized in that: The data acquisition component includes a temperature sensor (6), a pore pressure sensor (7), a normal stress sensor (8), a laser water level gauge (9) and a tube water level gauge (10); There are several temperature sensors (6), some of which are arranged in the test box (1) for detecting the ambient temperature, some of which are arranged at different depths of the water body for detecting the water body temperature at different depths, and the remaining temperature sensors (6) are arranged in soil layers at different heights for detecting the soil body temperature at different heights; Pore ​​pressure sensors (7) and normal stress sensors (8) are also provided at different heights of the soil layer; The tubular water level gauge (10) is in communication with the drainage pipe (5); the laser water level gauge (9) is arranged on the top of the test box (1) and faces the water surface.

7. The test device for indoor simulation of freeze-thaw cycles on seasonally frozen river slopes according to claim 1, characterized in that: The drain pipe (5) is provided with an outlet flow regulating valve (11), and the end of the drain pipe (5) facing away from the test box (1) is inserted into a water reservoir (13). A centrifugal pump (14) is provided inside or outside the water reservoir (13). The outlet pipeline of the centrifugal pump (14) is communicated with the water inlet pipe (4), and the water inlet pipe (4) is provided with an inlet flow regulating valve (12).

8. The test device for indoor simulation of freeze-thaw cycles of seasonally frozen river slopes according to claim 1, characterized in that: The contact surface between the soil layer and the inner wall of the test box (1) is provided with a nanofiber porous ceramic water-permeable filter layer (15); the end surface of the drainage pipe (5) located inside the test box (1) is also covered with the nanofiber porous ceramic water-permeable filter layer (15); and a soil drainage pipe (16) is provided at the bottom of the soil layer.

9. The test device for indoor simulation of freeze-thaw cycles of seasonally frozen river slopes according to claim 1, characterized in that: The top of the test box (1) can be opened and closed, and the front and rear sides are made of light-transmitting and low-temperature-resistant polycarbonate plates; the left and right sides, top and bottom of the test box (1) are provided with thermal insulation layers; and the side wall of the test box (1) that contacts the soil layer and is away from the water body is provided with a plurality of sampling lattice doors (17) distributed up and down.

10. A test method for indoor simulation of freeze-thaw cycles on seasonally frozen river slopes, based on the test device for indoor simulation of freeze-thaw cycles on seasonally frozen river slopes according to any one of claims 1 to 9, characterized in that: include: Prepare soil samples according to the test purpose, and fill the soil samples in layers according to the set slope or implant the original soil into the test box (1); The sensors of the data acquisition assembly are placed at respective set positions according to the test layout, and a heating element (3) is provided on the contact surface between the soil layer and the bottom of the water body; Filling the test chamber (1) with water so that the water level is accurately adjusted to the base water level; The freeze-thaw cycle process is simulated, specifically: in the freezing stage and the stable freezing stage, the environment temperature adjustment component (2) cools down or keeps the environment in the test box (1) constant according to the set temperature change curve, and the drain pipe (5) discharges the water in the test box (1) according to the set water level change curve; at the same time, the heating component (3) heats the bottom of the water body, so that the combined effect of the environment temperature and the bottom water temperature can achieve the expected freezing thickness, simulating the stratification scene of the surface freezing and the lower free liquid layer in the seasonally frozen river; in the melting stage, according to the set temperature change curve, the environment temperature adjustment component (2) heats the environment in the test box (1), and according to the set water level change curve, the water inlet pipe (4) replenishes the water in the test box (1); Data collection and analysis: During the freeze-thaw cycle, the readings of each sensor are collected and data analysis is performed based on the collected data.

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