A quantitative analysis method for water-heat-force of wicking geotextile regulating soil freeze-thaw cycle process

Abstract

The present application belongs to the technical field of special soil quantitative analysis, and proposes a water-heat-force quantitative analysis method for regulating and controlling soil body freeze-thaw cycle process by wicking geotextile, and the specific steps are as follows: triaxial shear test of soil under freeze-thaw cycle conditions is carried out to obtain soil body cohesion force degradation equation under water-heat condition; the control equations of temperature field and moisture field are converted into theoretical equations with saturation S as independent variable to realize two field coupling; the coupling relationship between wicking geotextile and moisture field is established; and the calculation method of stress field, temperature field, moisture field and wicking geotextile is written into numerical simulation software for full coupling. The present application is established by indoor test combined with calculation theory derivation, realizes effective simulation of the regulation and control effect of wicking geotextile on roadbed water content, determines the best laying position and laying method of wicking geotextile in the process of regulating and controlling roadbed drainage, improves the efficiency of wicking geotextile in regulating and controlling roadbed water content, and reduces the engineering cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of special soil quantitative analysis, and relates to a water-heat-force quantitative analysis method for regulating water-heat-force in a freezing-thawing cycle process of soil by wicking geotextile. BACKGROUND

[0002] Under the background of global warming, the unstable permafrost range of seasonal freezing and thawing in permafrost regions increases year by year. The strong capillary action and temperature gradient drive the water migration and accumulation in the roadbed, which leads to the phenomena of melting settlement, mud boiling, local instability and collapse in high-cold regions, resulting in the service life of roads of all grades being far lower than the design life, and the annual maintenance cost being huge. One of the effective measures for preventing and controlling roadbed frost damage is to prevent water from flowing to the freezing front. However, due to the influence of the excess pore water pressure of the soil body, the existing drainage design method is mainly used for processing gravity water and cannot effectively drain the capillary water from the roadbed structure.

[0003] At present, in the field of frozen soil, the method of coupling of water field, stress field and temperature field is usually used to study the related problems in the field. However, since the wicking geotextile is a humidity control material, there is a fundamental difference between the wicking geotextile and the soil, which makes the current water migration theory of the wicking geotextile not yet completely constructed, resulting in no water-heat-force calculation method based on the wicking geotextile regulating the water content of the soil body. Therefore, in the engineering application, it is difficult to find the best laying position and laying method of the wicking geotextile in the roadbed, and it is difficult to effectively characterize the regulation effect of the wicking geotextile on the frost heaving and thawing settlement of the soil body, which is easy to cause the waste of resources. SUMMARY

[0004] The application provides a water-heat-force quantitative analysis method for regulating a freezing-thawing cycle process of a soil body by wicking geotextile, which characterizes the regulation effect of the wicking geotextile on the frost heaving and thawing settlement of the soil body from the quantitative point of view, and reveals the action mechanism of the wicking geotextile on the water migration, temperature regulation and settlement evolution of the soil body, thereby providing theoretical and technical support for the prevention and control of the frost damage of the high-cold roadbed in the frozen soil region and the long-term service performance maintenance.

[0005] In order to achieve the above purpose, the technical scheme adopted by the application is as follows.

[0006] S1, triaxial shear tests of the soil body under the freezing-thawing cycle condition are carried out for the engineering region, the saturation, the freezing-thawing cycle number and the freezing temperature are taken as the independent variables, and the soil body cohesion degradation equation under the water-heat condition is obtained through polynomial fitting;

[0007] S2, based on the theoretical expression of unfrozen water content and initial moisture content, the temperature field control equation and the moisture field control equation are transformed into the theoretical equation with saturation S as the independent variable, realizing the coupling of temperature field and moisture field;

[0008] S3, indoor wicking geotextile-soil column test is carried out, the relationship between soil saturation and wicking geotextile water conductivity is established, the boundary condition of wicking geotextile humidity control is determined, and the coupling relationship between wicking geotextile and moisture field is established;

[0009] S4, the calculation method of stress field, temperature field, moisture field and wicking geotextile in S1, S2 and S3 is written into COMSOL Multiphysics software for full coupling, so as to realize the quantitative analysis of the regulation of wicking geotextile on subgrade deformation, temperature and humidity under different conditions.

[0010] As preferred, S1 specifically comprises the following steps:

[0011] S11, prepare triaxial test soil sample, determine the saturation, freezing temperature and freeze-thaw cycle number of soil according to the environmental conditions and basic parameters of actual engineering, carry out consolidated un-drained triaxial test, and obtain the stress-strain relationship and strength parameter variation law of soil under different conditions;

[0012] S12, based on the obtained stress-strain relationship, the relationships of cohesion-saturation, cohesion-cycle number and cohesion-freezing temperature are established according to Mohr-Coulomb strength theory, and the influence characteristics and law trend of each factor on cohesion are obtained;

[0013] S13, analyze the influence weight of different saturation, cycle number and freezing temperature on cohesion through decision tree model in supervised machine learning algorithm, and obtain the most significant factor affecting soil cohesion;

[0014] S14, obtain the cohesion degradation equation through polynomial coupling, that is, c=y(S, T, n), wherein S is saturation, T is temperature, and n is cycle number.

[0015] As preferred, S2 specifically comprises the following steps:

[0016] S21, the theoretical expression of unfrozen water content and initial moisture content is: , wherein T is temperature, ω0 is the mass moisture content of unfrozen water at freezing temperature T, ω0 is the initial mass moisture content of soil, B is an empirical coefficient related to solid-liquid ratio, and T is the freezing temperature of soil. u f

[0017] ​​S22. The temperature field governing equation is transformed into an equation with saturation S as the independent variable: In the formula, C is the volumetric specific heat capacity, ρ i Where S is the density of ice, S is the degree of saturation, and θ is the density of ice. s and θ r Let T and λ represent the saturated moisture content and residual moisture content, respectively, where T is the temperature, λ is the thermal conductivity, and B is the thermal conductivity. i The solid-liquid ratio;

[0018] S23. The governing equation for the moisture field is transformed into an equation with saturation S as the independent variable: , In the formula, q represents the flow rate. For the matric suction of the soil, k(h) m ) is the permeability coefficient function, h is the matrix suction head, and α is a parameter related to the air intake value in the geotechnical engineering VG model.

[0019] As a preferred option, S3 specifically includes the following steps:

[0020] S31. Before the test, the basic properties of the soil were measured;

[0021] S32. Prepare test specimens. Prepare three parallel standard specimens for each moisture content sample. To obtain the initial state of the soil column, set up a test specimen for each moisture content sample. Place all test specimens in a curing chamber at 20℃ and 30% humidity. Place all test specimens on a mass sensor with an accuracy of 0.1g and monitor the mass change of the test specimens in real time. When the mass of the test specimens decreases to a stable level, the soil column and air humidity reach equilibrium.

[0022] S33. Conduct the experiment. At the same time every day, take out each group of samples from the curing box in sequence, record the mass with an electronic scale, and then quickly put them back into the curing box.

[0023] S34. Based on the changes in the mass of soil columns with different moisture contents over time obtained from monitoring, calculate the daily volumetric moisture content of different soils. In the curve of the change in volumetric moisture content of soil over time, the line connecting the start and end points is regarded as the average drainage rate of the core-absorbing geotextile, and then it is converted into the matrix suction head.

[0024] S35. According to the basic soil property formula, the soil moisture content is converted into saturation. This yields the average water conductivity of the wicking geotextile corresponding to soils with different initial moisture contents. Through nonlinear fitting, the relationship between the soil moisture content and the wicking geotextile water conductivity is obtained, establishing the relationship between soil saturation and the wicking geotextile water conductivity. .

[0025] As preferred, the basic properties of the soil body in S31 include the liquid limit, plastic limit, optimum moisture content, maximum dry density, mineral composition, saturated moisture content, residual moisture content, and soil-water characteristic curve of the soil body.

[0026] As preferred, S4 specifically includes the following steps:

[0027] S41, four-field coupling is realized by PDEs self-defined coefficient type partial differential equation module and solid mechanics module;

[0028] S42, in the solid mechanics field, the soil body is regarded as an elastic-plastic model, and the frost-heave force formula is: , wherein E is the Young's modulus, μ is the Poisson's ratio, is the strain, , wherein: η(θ i ) is the frost-heave coefficient, which is affected by the volume ice content in the soil body, and a semi-empirical formula for determining the value of η(θ );

[0029] S43, parameter setting of the solid mechanics field, the top end boundary is set as a free end, and the remaining boundaries are set as fixed constraints, which are used to observe the deformation amount of the soil body frost-heave thaw-settlement at the top end; the cohesion value is set as the soil body cohesion degradation equation in S1, and the internal friction angle value is set as the average value of all triaxial shear test results in S1; when the cohesion equation is embedded, the saturation S in the cohesion formula is the real-time calculation result of the moisture field;

[0030] S44, in the moisture field, the moisture field equation is: , wherein z is the gravity potential, is the matric potential, k is the permeability coefficient, ρ i is the density of ice, ρ ω is the density of water, θ u is the unfrozen water content; the outer boundary of the soil column is a zero flux boundary, the bottom end boundary is set as a Dirichlet boundary when simulating the continuous water supply condition, and the saturation S is set as a constant value 0.99, while the bottom end boundary is also set as a zero flux boundary when simulating the closed condition;

[0031] S45, in the temperature field, the control equation of the temperature field is: , wherein C is the volume specific heat capacity, ρ i is the density of ice, S is the saturation, θ s and θ r respectively represent the saturated moisture content and the residual moisture content, T is the temperature, λ is the thermal conductivity, B i is the solid-liquid ratio; during the construction of the temperature field, the top end boundary is subjected to a freeze-thaw cycle temperature condition T by adding a 2cm long boundary on both sides, so as to simulate the effect of the upper temperature control disc with a certain thickness on the top of the soil column, and the temperature rising and falling rate is 2℃ / h, and the other boundaries are constant temperature 10℃;

[0032] S46, the control equation of the wicking geotextile field is: , the equation is obtained by coupling the wicking geotextile-soil column test;

[0033] S47, in the water-heat-force coupling calculation process of COMSOL, the volume ice content rate is converted into the frost heaving coefficient by using the built-in IF function, and the deformation coefficient is input into the expansion coefficient of COMSOL, and the numerical simulation of the frost heaving and thawing process of unsaturated frozen soil is realized by using the transient solver.

[0034] Compared with the prior art, the advantages and positive effects of the present application are:

[0035] The water-heat-force quantitative analysis method for regulating the freezing and thawing cycle process of the soil body by the wicking geotextile provided by the present application can realize the wicking geotextile-water-heat-force multi-field coupling in the subgrade in the high-cold frozen soil area, the coupling method is derived and established by combining the indoor test with the calculation theory, the physical structure of the model is closer to the actual situation, the precision is high, the calculation speed is fast, the regulation effect of the wicking geotextile on the water content of the subgrade can be effectively simulated, the best laying position and the best laying method of the wicking geotextile in the process of regulating the drainage of the subgrade can be determined, so that the efficiency of the wicking geotextile in regulating the humidity of the subgrade is improved, and the engineering cost is reduced; the present application is not only suitable for the high-cold frozen soil subgrade, but also suitable for other soil subgrades on the basis of parameter setting and calibration, and has a wide range of application. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0037] Figure 1 It is a step flow chart of the water-heat-force calculation method for regulating the water content change of the soil body by the wicking geotextile;

[0038] Figure 2 It is a theoretical diagram of the wicking geotextile-water-heat-force multi-field coupling method provided by the embodiment;

[0039] Figure 3 It is a schematic diagram of the wicking geotextile-soil column test provided by the embodiment;

[0040] Figure 4 It is a flow chart of the wicking geotextile-soil column test and calculation theory provided by the embodiment;

[0041] Figure 5 Time-history curve of maximum frost heave amount of MWG subgrade at different positions;

[0042] Figure 6 Schematic diagram of variation law of maximum frozen depth Z;

[0043] Figure 7 Schematic diagram of variation law of total frost heave amount z;

[0044] Figure 8 Schematic diagram of variation law of average frost heave amount η. DETAILED DESCRIPTION

[0045] In order to more clearly understand the above-mentioned purposes, features and advantages of the present application, the present application will be further described below in combination with the drawings and embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict. For the convenience of description, the terms of “up”, “down”, “left”, “right” appear below only represent the up, down, left and right directions consistent with the drawings themselves, and do not limit the structure.

[0046] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present application, however, the present application can also be implemented in other ways different from those described herein, and therefore, the present application is not limited to the specific embodiments disclosed in the following description.

[0047] As shown in the embodiments, the present application provides a water-heat-force quantitative analysis method for regulating soil body freeze-thaw cycle process by wicking geotextile, which comprises the following specific steps: Figures 1-4

[0048] S1, triaxial shear test of soil under freeze-thaw cycle conditions is carried out, saturation, freeze-thaw cycle number and freezing temperature are taken as independent variables respectively, and a soil body cohesion force degradation equation under water-heat conditions is obtained through polynomial fitting to obtain a calculation method of stress field;

[0049] S2, based on the theoretical expression of unfrozen water content and initial moisture content, the temperature field control equation and the water field control equation are respectively converted into theoretical equations with saturation S as the independent variable, the coupling of the temperature field and the water field is realized, and the calculation methods of the temperature field and the water field are obtained;

[0050] S3, indoor wicking geotextile-soil column test is carried out, the relationship between soil saturation and wicking geotextile water conductivity is established, the boundary condition of wicking geotextile humidity control is determined, the coupling relationship between wicking geotextile and water field is established, and the calculation method of wicking geotextile is obtained;

[0051] ​S4, write the calculation method of stress field, temperature field, moisture field and wicking geotextile in COMSOL Multiphysics software, fully coupled, realize the quantitative analysis of the regulation effect of wicking geotextile on subgrade deformation, temperature and humidity under different conditions.

[0052] S1 specifically includes the following steps:

[0053] S11, prepare triaxial test soil samples, according to the specification requirements, use static compaction method to prepare standard triaxial test soil samples with diameter of 39.1mm and height of 80mm, according to the environmental conditions and basic parameters of the actual engineering, determine the saturation, freezing temperature and freeze-thaw cycle number of the soil, carry out consolidation undrained triaxial test, get the stress-strain relationship and strength parameter variation law of the soil under different conditions;

[0054] S12, based on the obtained stress-strain relationship, according to the Mohr-Coulomb strength theory, respectively establish the relationship of cohesion-saturation, cohesion-cycle number and cohesion-freezing temperature, get the influence characteristics and law trend of each factor on cohesion;

[0055] S13, the machine learning algorithm used is mainly the decision tree model in supervised machine learning algorithm, which analyzes the influence weight of different saturation, cycle number and freezing temperature on cohesion, and gets the most significant factor affecting the cohesion of soil;

[0056] S14, the cohesion degradation equation obtained by polynomial coupling is c=y (S, T, n), wherein S is saturation, T is temperature, and n is cycle number, which are independent variables.

[0057] S2 specifically includes the following steps:

[0058] S21, the theoretical expression of unfrozen water content and initial moisture content is: , wherein T is temperature (℃), ω0 is the mass moisture content of unfrozen water at freezing temperature T (%), ω u is the initial mass moisture content of soil (%), B is an empirical coefficient related to solid-liquid ratio, T f is the freezing temperature of soil (℃);

[0059] S22, the temperature field control equation is transformed into the independent variable equation with saturation S as: , wherein C is the volume specific heat capacity, ρ i is the density of ice, S is the saturation, θ s and θ r represent the saturated moisture content and residual moisture content respectively, T is the temperature, λ is the thermal conductivity, B i is the solid-liquid ratio;

[0060] S23, the moisture field control equation is converted into an independent variable equation with saturation S as: , ; in the formula, q is the flow rate, is the matric suction of the soil body, k(h m ) is the permeability coefficient function, h is the matric suction water head, and a is a parameter related to the air entry value in the VG model of geotechnical engineering.

[0061] S3 specifically includes the following steps:

[0062] S31, before the test, that is, before the indoor moisture migration test under the action of the geotextile, the basic properties of the soil body are measured according to the “Standard for Soil Test Methods” (GB / T 50123-2019), and the basic properties of the soil body include the liquid limit, plastic limit, optimum water content, maximum dry density, mineral composition, saturated water content, residual water content, and soil-water characteristic curve of the soil body and other physical properties;

[0063] S32, the test piece is made, three parallel standard test pieces are made for each water content sample, in order to obtain the initial state of the soil column, one test test piece is set for all water content samples, and all test samples are placed in a curing box with a temperature of 20℃ and a humidity of 30%, all test samples are placed on a mass sensor with a precision of 0.1g, and the mass change of the test sample is monitored in real time; if the mass of the test sample decreases to a stable level, the soil column and the air humidity reach equilibrium;

[0064] S33, the test is carried out, and every day at the same time, each group of samples is taken out from the curing box in turn, the mass is recorded by an electronic scale, and then it is quickly put back into the curing box to reduce the influence of the measurement environment on the moisture migration process;

[0065] S34, according to the change of the mass of the soil column with different water contents with time obtained by monitoring, the volume water content of each soil body is calculated every day, and in the change curve of the volume water content of the soil body with time, the connecting line of the starting point and the ending point is regarded as the average drainage rate of the wicking geotextile, and then it is converted into the matric suction water head;

[0066] S35, according to the formula of the basic properties of the soil, the water content of the soil is converted into the saturation, and thus the average water conductivity rate of the wicking geotextile corresponding to the soil body with different initial water contents is obtained, the soil water content and the water conductivity rate of the wicking geotextile are obtained by nonlinear fitting, and the relationship between the saturation of the soil and the water conductivity rate of the wicking geotextile is established, that is: .

[0067] S4 specifically includes the following steps:

[0068] S41, four-field coupling is realized by PDEs self-defined coefficient type partial differential equation module and solid mechanics module; in the process of four-field coupling, the model size, each boundary condition and the arrangement of monitoring points should be consistent with the test.

[0069] S42, in the solid mechanics field, the soil body is regarded as an elastic-plastic model, and the frost heaving force formula is: , wherein E is the Young's modulus, μ is the Poisson's ratio, is the strain, the formula of which is: , wherein: η (θ i ) is the frost heaving coefficient, which is affected by the volume ice content in the soil body, and the semi-empirical formula for determining the value thereof is, ;

[0070] S43, in the solid mechanics field, the top end boundary is set as a free end, and the remaining boundaries are set as fixed constraints, which are used to observe the deformation amount of the soil body frost heaving and thawing settlement at the top end; the cohesion value is assigned as the soil body cohesion degradation equation in S1, and the internal friction angle value is the average value of all triaxial shear test results in S1; when the cohesion equation is embedded, the saturation S in the cohesion formula is the real-time calculation result of the moisture field;

[0071] S44, in the moisture field, the moisture field equation is: , wherein: z is the gravity potential, is the matrix potential, k is the permeability coefficient, ρ i is the density of ice, ρ ω is the density of water, θ u is the unfrozen water content; the outer boundary of the soil column is a zero flux boundary, in the simulation of continuous water supply conditions, the bottom end boundary is set as a Dirichlet boundary, and the saturation S is set as a constant value 0.99, and in the simulation of closed conditions, the bottom end boundary is also set as a zero flux boundary;

[0072] S45, in the temperature field, the control equation of the temperature field is: In the equation: C is the volume specific heat capacity, ρ i is the density of ice, S is the saturation, θ s and θ r represent the saturated water content and residual water content respectively, T is the temperature, λ is the thermal conductivity, B i is the solid-liquid ratio; in the process of building the temperature field, the top end boundary is subjected to the freeze-thaw cycle temperature condition T by adding two 2cm long boundaries on both sides, so as to simulate the effect of the upper temperature control disc with a certain thickness on the top of the soil column, the temperature rising and falling rate is 2℃ / h, and the other boundaries are constant temperature 10℃;

[0073] S46, the control equation of the wicking geotextile field is: The equation is obtained by coupling the wicking geotextile-soil column test; the specific equation expression should be adjusted according to the results of the designed test;

[0074] S47、In the process of COMSOL water-thermal-force coupling calculation, the volume ice content rate is converted into frost heaving coefficient by using the built-in IF function, and the deformation coefficient is input into the expansion coefficient of COMSOL, and the numerical simulation of the frost heaving and thawing settlement process of unsaturated frozen soil is realized by using the transient solver.

[0075] According to the different η values defined in the design specification corresponding to the subgrade frost heaving grade, different working conditions of subgrade are divided into five grades: no frost heaving (grade I), weak frost heaving (grade II), frost heaving (grade III), strong frost heaving (grade IV) and special strong frost heaving (grade V). Taking grade III subgrade as an example, through numerical simulation test of M WG at different positions, it is found that the position of M WG will significantly affect the change of the maximum frost heaving amount of subgrade. The vertical distance from the top of M WG to the pavement boundary is defined as H (m). Select H = 3.0, 3.5, 4.0, 4.5, 5.0, 5.5 (m), and the time history waterfall diagram of the frost heaving amount of each group is shown in Figure 5 From the figure, it can be seen that M WG significantly reduces the maximum frost heaving amount of subgrade, and the larger the number of freeze-thaw cycles, the greater the reduction of the maximum frost heaving amount of subgrade controlled by M WG. Projecting the maximum frost heaving amount of each group of working conditions into the plane coordinate of frost heaving amount and H, it can be found that when H≤4.5m, the maximum frost heaving amount gradually decreases with the increase of H, and the decreasing amplitude becomes lower and lower, which is due to the fact that when the depth of M WG increases, its capillary barrier can more effectively intercept the rising capillary water. However, when H>4.5m, the maximum frost heaving amount increases in the opposite direction with the increase of H, which is due to the fact that when M WG is buried too deep, the capillary barrier is out of the active area of freezing front, which weakens the inhibition effect on the growth of ice lens. However, the frost heaving amount of all test groups is still significantly lower than that of the control group, and the overall effect of M WG on the prevention and control of subgrade frost heaving is still reflected, and H=4.5m is the optimal solution for engineering.

[0076] Based on this, the M WG prevention and control effect analysis of H=3.0, 3.5, 4.0, 4.5, 5.0, 5.5 (m) of grade II, grade III, grade IV and grade V subgrade is carried out respectively, and the curves of η, z and Z varying with H of different safety grades are drawn as shown in Figures 6-8 The mathematical expressions of the three can be expressed as: , wherein z is the total frost heaving amount of soil (m), Z is the corresponding maximum frozen depth (m) excluding the frost heaving amount. As can be seen from the figure, Z presents a change trend of first decreasing and then slowly increasing with the increase of H, and z presents a change trend of first decreasing and then remaining stable with the increase of H, and the change law of the 2nd subgrade is not obvious due to the low base. Finally, the change law of η calculated based on S42 is shown in the following table Figure 8 When the MWG is laid to be 4.5-5 m away from the top road surface boundary, the η has the largest decrease. At the same time, it can be seen that the frost heaving grades of all the subgrades can be reduced by one level on the basis of the original basis when H=4.5-5 m, and for the 2nd subgrade, the frost damage control requirements can be met, and H=4.5 m is taken. For other grades of subgrades, 1 layer of MWG cannot meet the control requirements, that is, subsequent analysis of the laying conditions of multiple layers of MWG needs to be carried out.

[0077] For the most unfavorable working condition of each safety grade subgrade, the control effect of 1 layer of MWG at the optimal laying position is given priority to, and the control effect of 2 layers of MWG at the optimal laying position and spacing is considered secondly. Finally, the following optimal construction parameters that can meet the safety requirements of the frost heaving subgrade are obtained: the 1st subgrade does not need to take any control measures, 1 layer of MWG is laid under the 2nd subgrade, which is 4.5 m away from the road surface, 2 layers of MWG are laid under the 3rd-4th subgrade, the top layer of MWG is 3.5 m away from the road surface, and the spacing between the 2 layers of fabric is 2 m, and 2 layers of MWG are laid under the 5th subgrade, the top layer of MWG is 3 m away from the road surface, and the spacing between the 2 layers of fabric is 2.5 m.

[0078] The application discloses a water-heat-force coupling quantitative analysis method for regulating soil moisture content change by wicking geotextile, which can realize the wicking geotextile-water-heat-force multi-field coupling in a subgrade in an alpine permafrost region, and the coupling method is derived and established by combining indoor tests with calculation theories, so that the physical structure of the model is closer to the actual situation, the method has high precision and fast calculation speed, can realize effective simulation of the regulation effect of the wicking geotextile on the moisture content of the subgrade, and can determine the optimal laying position and the optimal laying method of the wicking geotextile in the process of regulating the drainage of the subgrade, so that the efficiency of the wicking geotextile in regulating the humidity of the subgrade is improved, and the engineering cost is reduced. The application is not only suitable for the alpine permafrost subgrade, but also suitable for other soil subgrades by setting and calibrating parameters on the basis of the alpine permafrost subgrade, so that the application range of the model is also expanded.

[0079] The above description is only a preferred embodiment of the present application, and is not intended to limit the present application in other forms. Any skilled person in the art can modify or change the above disclosed technical content into equivalent embodiments applied to other fields, but any simple modification, equivalent change and modification made on the basis of the technical essence of the present application to the above embodiments still belongs to the protection scope of the technical solution of the present application.

Claims

1. A quantitative water-thermal-mechanical analysis method for regulating the freeze-thaw cycle process of soil using wicking geotextiles, characterized in that, The specific steps include the following: S1. Triaxial shear tests were conducted on soil under freeze-thaw cycles. Using saturation, number of freeze-thaw cycles, and freezing temperature as independent variables, a soil cohesion degradation equation under water-thermal conditions was obtained through polynomial fitting. The soil cohesion degradation equation was used to assign a value to the cohesion of the solid mechanical field in the fully coupled stage. The internal friction angle of the solid mechanical field was taken as the average value of all triaxial shear test results in S1. The saturation S in the soil cohesion degradation equation was the result of real-time calculation of the moisture field. S2. Based on the theoretical expressions of unfrozen water content and initial moisture content, the temperature field control equation and the moisture field control equation are transformed into theoretical equations with saturation S as the independent variable, thereby realizing the coupling of the temperature field and the moisture field. S3. Conduct indoor wicking geotextile-soil column tests. Based on the changes in the mass of soil columns with different moisture contents over time, calculate the daily moisture content of different soils. In the curve of soil moisture content change over time, the line connecting the start and end points is regarded as the average water conductivity of the wicking geotextile. According to the basic soil property formula, convert the volumetric moisture content of the soil into saturation, thereby obtaining the average water conductivity of the wicking geotextile corresponding to soils with different saturations. Determine the boundary conditions for the moisture control effect of the wicking geotextile and establish the coupling relationship between the wicking geotextile and the moisture field. S4. The calculation methods of stress field, temperature field, moisture field and wicking geotextile in S1, S2 and S3 are written into COMSOL Multiphysics software and fully coupled to realize the quantitative analysis of the regulatory effect of wicking geotextile on subgrade deformation, temperature and humidity under different conditions.

2. The method for quantitative analysis of water-thermal-mechanical processes in regulating soil freeze-thaw cycles using wicking geotextiles according to claim 1, characterized in that, S1 specifically includes the following steps: S11. Prepare triaxial test soil samples. Based on the environmental conditions and basic parameters of the actual project, determine the soil saturation, freezing temperature and number of freeze-thaw cycles. Conduct consolidated undrained triaxial tests to obtain the stress-strain relationship and strength parameter variation law of the soil under different conditions. S12. Based on the obtained stress-strain relationship, according to the Mohr-Coulomb strength theory, the relationships between cohesion-saturation, cohesion-cycle number, and cohesion-freezing temperature are established respectively, and the influence characteristics and trends of each factor on cohesion are obtained. S13. By using the decision tree model in the supervised machine learning algorithm, analyze the influence weights of different saturation, number of cycles, and freezing temperature on cohesion, and obtain the most significant factors affecting soil cohesion. S14. The cohesion degradation equation obtained through polynomial coupling, i.e., c=y(S, , n), where S is the saturation degree; is the freezing temperature; n is the number of freeze-thaw cycles.

3. The method for quantitative analysis of water-thermal-mechanical processes in regulating soil freeze-thaw cycles using wicking geotextiles according to claim 2, characterized in that, S2 specifically includes the following steps: S21. The theoretical expression for the relationship between unfrozen water content and initial moisture content is: In the formula, T is the temperature. f Let ω be the freezing temperature of the soil, ω0 be the mass water content of the soil at temperature T, and ω u denoted as the initial mass water content of the soil, and B is an empirical coefficient related to the solid-liquid ratio; S22. The temperature field governing equation is transformed into an equation with saturation S as the independent variable: In the formula, C is the volumetric specific heat capacity, ρ i Where S is the density of ice, S is the degree of saturation, and θ is the density of ice. s and θ r Let T and λ represent the saturated moisture content and residual moisture content, respectively, where T is the temperature, λ is the thermal conductivity, and B is the thermal conductivity. i The solid-liquid ratio; S23. The governing equation for the moisture field is transformed into an equation with saturation S as the independent variable: , In the formula, q represents the flow rate. For the matric suction of the soil, k(h) m ) is the permeability coefficient function, h is the matrix suction head, and α is a parameter related to the air intake value in the geotechnical engineering VG model.

4. The method for quantitative analysis of water-thermal-mechanical processes in regulating soil freeze-thaw cycles using wicking geotextiles according to claim 3, characterized in that, S3 specifically includes the following steps: S31. Before the test, the basic properties of the soil were measured; S32. Prepare test specimens. Prepare three parallel standard specimens for each moisture content sample. To obtain the initial state of the soil column, set up a test specimen for each moisture content sample. Place all test specimens in a curing chamber at 20℃ and 30% humidity. Place all test specimens on a mass sensor with an accuracy of 0.1g and monitor the mass change of the test specimens in real time. When the mass of the test specimens decreases to a stable level, the soil column and air humidity reach equilibrium. S33. Conduct the experiment. At the same time every day, take out each group of samples from the curing box in sequence, record the mass with an electronic scale, and then quickly put them back into the curing box. S34. Based on the changes in the mass of soil columns with different moisture contents over time obtained from monitoring, calculate the daily volumetric moisture content of different soils. In the curve of the change in the volumetric moisture content of the soil over time, the line connecting the start and end points is regarded as the average water conductivity of the core-absorbing geotextile. Convert the volumetric moisture content of the soil into the matrix water absorption head. S35. According to the basic soil property formula, the volumetric water content of the soil is converted into saturation to obtain the average water conductivity of the wicking geotextile corresponding to soils with different saturations. Then, the volumetric water content of the soil and the water conductivity of the wicking geotextile are nonlinearly fitted to establish the relationship between the soil saturation and the water conductivity of the wicking geotextile, that is: .

5. The method for quantitative analysis of water-thermal-mechanical processes in regulating soil freeze-thaw cycles using wicking geotextiles according to claim 4, characterized in that, The basic properties of soil in S31 include the liquid limit, plastic limit, optimum moisture content, maximum dry density, mineral composition, saturated moisture content, residual moisture content, and soil-water characteristic curve.

6. The method for quantitative analysis of water-thermal-mechanical processes in regulating soil freeze-thaw cycles using wicking geotextiles according to claim 5, characterized in that, S4 specifically includes the following steps: S41. Four-field coupling is achieved through the PDEs custom coefficient type partial differential equation module and solid mechanics module. S42. In a solid mechanics field, considering the soil as an elastoplastic model, the formula for frost heave force is: In the formula, E is Young's modulus and μ is Poisson's ratio. In response, In the formula: T is the temperature. Let η(θ) be the freezing temperature. i The frost heave coefficient is affected by the volumetric ice content in the soil. A semi-empirical formula for determining its value is: ; S43. Setting parameters for the solid mechanics field: Set the top boundary as a free end and the other boundaries as fixed constraints to observe the deformation of the soil at the top due to frost heave and thaw settlement. S44. In a moisture field, the moisture field equation is: In the formula: z is the gravitational potential. ρ is the matrix potential, k is the permeability coefficient, and ρ is the matrix potential. i It is the density of ice, ρ ω It is the density of water, θ u This refers to the unfrozen water content; the outer perimeter of the soil column is a zero flux boundary. When simulating continuous water replenishment, the bottom boundary is set as a Dirichlet boundary with a constant saturation value of 0.

99. When simulating closed conditions, the bottom boundary is also set as a zero flux boundary. S45. In a temperature field, the governing equation of the temperature field is: In the formula: C is the volumetric specific heat capacity, ρ i Where S is the density of ice, S is the degree of saturation, and θ is the density of ice. s and θ r Let T and λ represent the saturated moisture content and residual moisture content, respectively, where T is the temperature, λ is the thermal conductivity, and B is the thermal conductivity. i The solid-liquid ratio is used. During the construction of the temperature field, a temperature condition T is applied to the top boundary plus two 2cm long boundaries on both sides to simulate the effect of a temperature control plate with a certain thickness at the top of the soil column. The heating and cooling rate is 2℃ / h, and the other boundaries are kept at a constant temperature of 10℃. The governing equation for S46, the wicking geotextile field, is: This equation was obtained through coupling of wicking geotextile and soil column tests. S47. In the water-thermal-mechanical coupling calculation process of COMSOL, the volumetric ice content is converted into the frost heave coefficient using the built-in IF function. The deformation coefficient is then input into the expansion coefficient in COMSOL. The transient solver is used to realize the numerical simulation of the frost heave and thawing settlement process of unsaturated frozen soil.

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