Simulation method for seepage danger of levee driven by coupling characteristics of ice flood variable water level and frozen soil

Abstract

The present invention discloses a method for simulating the seepage danger of levees driven by the coupling of variable water levels during ice flood and frozen soil characteristics. A simulation model for the seepage danger of levees driven by the coupling of variable water levels during ice flood and frozen soil characteristics is constructed. The model includes a seepage analysis model for levees, a soil deformation safety analysis model for coupling the seepage field and strain field of the levee section, and a seepage stability analysis model for levees driven by the coupling of variable water levels during ice flood and frozen soil characteristics. The simulation analysis of the evolution process of the seepage danger of levees is realized by using the safety factor of the levee slope stability. The evolution law of the seepage danger of levees during ice flood is analyzed by selecting the levee danger index. The pore water pressure, XY-displacement and stability safety factor of the key points during the evolution process of the seepage danger of levees during ice flood are identified, and the slope stability threshold of the seepage danger of levees is quantitatively evaluated. Compared with the prior art, the present invention realizes the accurate simulation of the seepage danger of levees by combining the actual water level change and the frozen soil thickness during ice flood.

Description

Technical Field

[0001] The present invention relates to the technical field of computer digital technology assistance and emergency disaster prevention, and particularly relates to a method for simulating the seepage danger of levees driven by the coupling of ice flood variable water levels and frozen soil characteristics. Background Art

[0002] During the ice flood period, the influencing factors of the seepage danger of levees are complex and changeable. Especially during the freezing and thawing periods of the levee materials and the large gradient of water level and flow velocity changes during the river closure and opening periods, it is extremely easy to induce seepage and slope collapse dangers of the levees, and even trigger major flood and ice flood levee break disasters. Therefore, carrying out research on simulating the seepage danger of levees driven by the coupling of ice flood variable water levels and frozen soil characteristics is crucial for revealing the evolution mechanism of the seepage danger of levees driven by multi-factor coupling during the ice flood period and improving the theory of levee danger disaster prevention. The water level during the ice flood period usually has the characteristics of sudden rise and fall, large change gradient, frequent water level fluctuations, and long-term high water level state. After the river closure or during the river opening period, due to the sudden rise in temperature or increased rainfall, the ice floes melt rapidly, and the river water level rises by several meters or even higher within a short period (from several hours to several days), and the change rate can reach dozens of centimeters per hour. This sudden large-scale water level change greatly increases the risk of seepage failure of the levees. During the freezing period, the high water level state is maintained for a long time, usually lasting for several days to several weeks. When the ice jam is released, the water level drops suddenly, and the seepage pressure difference on both sides of the levee slope increases instantaneously, making it easy to occur seepage danger. In addition, in areas with large daily temperature differences, the ice floes melt faster during the day, the water level rises significantly, and the temperature drops at night, the melting slows down, and the water level is relatively stable or even drops. This non-uniformity of temperature change leads to steep rise and fall and frequent fluctuations of the ice flood water level. The frozen soil layer during the ice flood period is an important factor affecting the evolution of the seepage danger of levees. The change in the thickness of the frozen soil directly affects the permeability of the levee soil and the stability of the slope. The thickness of the frozen soil is affected by various factors such as temperature fluctuations and water level changes. During the ice flood period, the seasonal frozen soil gradually thickens, and then as the temperature rises, the frozen soil layer rapidly thins, and the frozen soil thickness differences in different regions are obvious. During the ice flood period, the rapid rise in the water level causes the surface water temperature to rise, accelerating the thawing process of the frozen soil. Especially during the critical period of ice jam formation and rupture, the rapid change in the water level significantly affects the temperature and structure of the frozen soil layer. As the frozen soil layer thaws, the surface runoff increases, leading to an increase in the river water level. At the same time, the permeability of the thawed frozen soil layer increases, making it easier for water to infiltrate, further affecting the dynamic change of the water level. The two are interrelated and interact with each other.

[0003] At present, scholars at home and abroad mainly focus on the simulation research of seepage hazards in levees during the flood season. The main influencing factors of levee seepage studied are the stable water level and the flood water level process with a constant change rate. The influencing factors studied are relatively single. Since the actual influencing factors of levee seepage hazards are complex and interrelated, the research on the influence of multiple factors on levee seepage hazards mostly considers the coupling of variable water levels and rainfall conditions during the flood season, and there are relatively few studies on other coupling conditions. Only a few scholars have studied the changes in levee hazard indicators under the action of ice flood by establishing a seepage model for levees during the ice flood season. The research results on the simulation of levee seepage hazards driven by the coupling of multiple factors during the ice flood season are relatively scarce. Summary of the Invention

[0004] Aiming at the problems existing in the existing research, the present invention proposes a method for simulating levee seepage hazards driven by the coupling of variable ice flood water levels and frozen soil characteristics, analyzes the change process of the rising and falling rates of ice flood water levels and frozen soil characteristics, and considers the influence of the characteristics of the change rate of water levels over time during the ice flood season, namely the sudden rise and rapid drop, on frozen soil levees. Based on basic theories such as seepage analysis, seepage-stress-strain coupling analysis, and stability analysis, a simulation model for levee seepage hazards driven by the coupling of variable ice flood water levels and frozen soil characteristics, a deformation safety analysis model based on the coupling of seepage field and strain field, and a numerical simulation model for levee stability based on seepage-strain coupling are constructed to identify the change characteristics of pore water pressure and XY-displacement during the evolution process of levee seepage hazards during the ice flood season, and quantitatively evaluate the slope stability threshold (minimum safety factor) of levee seepage hazards, providing support for revealing the mechanism of levee seepage changes driven by the coupling of variable ice flood water levels and frozen soil characteristics and improving the safety defense theory and method system for levee seepage hazards in the river channel during the ice flood season.

[0005] In order to achieve the above invention purpose, the present invention proposes the following technical solutions:

[0006] The present invention proposes a method for simulating levee seepage hazards driven by the coupling of variable ice flood water levels and frozen soil characteristics, mainly including the following technical contents:

[0007] S1, collection, processing and standardized compilation of basic data;

[0008] S2, analysis of variable ice flood water levels and frozen soil characteristics in the area to be simulated according to the collected basic data, including setting a combination of variable water level characteristics and frozen soil characteristics to represent the change process of levee seepage hazards, and obtaining the analysis results of variable ice flood water levels and frozen soil characteristics;

[0009] S3, setting the simulation scenario of levee seepage hazards during the ice flood season, determining the thickness of frozen soil for the simulated levee according to the analysis results of frozen soil characteristics, and determining the simulation boundary conditions according to the analysis results of variable ice flood water level characteristics, including hydraulic boundary conditions, stress boundary conditions and strain boundary conditions;

[0010] In S4, a seepage danger simulation model for levees driven by the coupling of variable water levels and frozen soil characteristics during the ice flood season is constructed. The cross-sectional dimensions of the frozen soil levee, the division of the cross-sectional network, the set material mechanics parameters, hydraulic parameters, and simulation boundary conditions are used as the inputs of the seepage danger simulation model for levees. Combining the basic data and the analysis results of the variable water levels and frozen soil characteristics during the ice flood season, the soil type, basic mechanics parameters, and hydraulic parameters of the levee are determined. The simulation analysis of the evolution process of the seepage danger of the levee is realized by using the safety factor of the levee slope stability. The construction of the seepage danger simulation model for levees specifically includes the following processes:

[0011] 4.1, Taking the control equation of two-dimensional saturated flow as the seepage analysis model for levees, the expression is:

[0012]

[0013] In the formula, H represents the total head, k x and k y represent the permeability coefficients in the x and y directions respectively, t represents time, m w represents the slope of the storage curve, γ w represents the unit weight of water, Q represents the increment or loss of water per unit volume, and the influence of Q is not considered;

[0014] The seepage analysis model for levees is solved by the finite element method, and the groundwater flow is described based on Darcy's law and the water balance equation.

[0015] 4.2, Establish a soil deformation safety analysis model for the coupling of the seepage field and strain field of the levee cross-section: According to the evolution process of the seepage danger of the levee simulated by the seepage analysis model for levees, analyze the deformation of the levee driven by the coupling of variable water levels and frozen soil characteristics during the ice flood season, and obtain the soil deformation safety analysis model for the coupling of the seepage field and strain field of the levee cross-section, including:

[0016] 1) The element balance equation for finite element coupling analysis, the expression is:

[0017] [K]{Δδ}+[L d {u w}={ΔF}

[0018] In the formula, [K] represents the element stiffness matrix, {Δδ} represents the nodal displacement vector, [L d represents the coupling matrix of the seepage field and strain field of the levee cross-section, {u w} represents the element pore water pressure vector, and {ΔF} represents the external force increment vector acting on the element;

[0019] 2) The flow equation for finite element coupling analysis, the expression is:

[0020]

[0021] In the formula, β represents the coupling coefficient, which describes the influence of soil deformation on seepage, [L f represents the seepage coupling matrix, Δt represents the time step, [K f represents the seepage hydraulic conductivity matrix, ω represents the relaxation coefficient, [M N represents the seepage mass matrix, {Δu w} represents the pore water pressure increment vector, {Q} |x+ΔM represents the external seepage at the position x + ΔM, {u w} |x represents the pore water pressure vector at the current position x;

[0022]

[0023] In the formula, E represents the elastic modulus, v represents the Poisson's ratio, K B represents the bulk modulus, h represents the thickness of the soil layer for seepage analysis, R represents the seepage resistance coefficient;

[0024] 3) The expression of the two-dimensional cross-section deformation finite element equation is:

[0025] ∫ A [B] T [C][B]dA{α} = bt∫ A <n> T dA + pt∫ L <n> T dL

[0026] where [C] represents the constitutive matrix, [B] represents the strain-displacement matrix, <n>Let the interpolation function be a row vector, {α} be the interpolation function column vector, A be the area of the element boundary, T represent matrix transpose, and L be the length of the element boundary;

[0027] 4) The expression for the strain-displacement matrix is:

[0028]

[0029] where N represents the shape function matrix, which is used to interpolate the displacement at the nodes, and N i represents the shape function of the i-th node. For an 8-node hexahedral element, N = {N 1 , N 2 , N 3 , …, N 8};

[0030] Thus, the two-dimensional plane stress-strain relationship of the levee structure is obtained;

[0031] 4.3. Based on the seepage field-strain field coupled soil deformation safety analysis model of the levee section constructed in 4.2, a seepage stability analysis model of the levee during the ice flood period driven by variable water levels coupling with frozen soil characteristics is established: On the basis of the seepage-strain coupled finite element simulation, the potential slip surface area is defined. Using the Morgenstern-Price method, a semi-sine function is selected as the inter-slice force function to satisfy the moment balance and force balance. By changing the ratio of the inter-slice shear force and normal force through an iterative process, the safety factors of different potential slip surfaces are finally obtained. Pay attention to the minimum safety factor and the corresponding slip surface to evaluate and analyze the stability of the levee slope. The expression for the safety factor of the levee slope stability is:

[0032]

[0033] where ∑T i represents the sum of shear stresses, Σ[cΔl i +(N i -u i Δl i )tanφ' e represents the sum of shear strengths, c represents the soil cohesion, N i , T i , u i , l i respectively represent the normal force, tangential force, pore water pressure, and slip surface length on the i-th soil strip, and φ' e represents the effective internal friction angle of the soil;

[0034] S5. Simulate the evolution process of seepage hazards of the levee during the ice flood period:

[0035] 5.1, Simulation process of seepage calculation and analysis for the levee: Input the initial boundary conditions, simulate the seepage inside the levee under the initial lowest water level condition, and considering the actual water level change process and frozen soil thickness during the ice flood season, pair different ice flood variable water level processes with different frozen soil thicknesses, set various variable rate water level boundary conditions on the water-facing side of the levee, and calculate the distribution and change of water flow in the levee soil under different working conditions through seepage analysis;

[0036] 5.2, Simulation process of stress and deformation conditions of the levee: Determine the stress and strain boundary conditions of the soil, combine with the calculation results of seepage analysis, consider the influence of pore water pressure of water flow on the stress state of the levee, and simulate the stress and deformation conditions of the soil under each working condition;

[0037] 5.3, Simulation process of changes in levee slope stability: Analyze the possible slip surfaces inside the levee during the water level change process, determine the positions and ranges of the inlet and outlet of the slip surface; on the basis of seepage analysis and seepage-stress strain coupling analysis, combine with the limit equilibrium theory analysis, simulate and calculate the change process of the slope safety factor under the coupling of variable water level and frozen soil characteristics, and identify the key slip surface with the lowest slope safety factor and potential instability areas and seepage hazards;

[0038] S6, Conduct analysis on the evolution law of seepage hazards of the levee during the ice flood season:

[0039] Select levee hazard indicators to analyze the evolution law of seepage hazards of the levee during the ice flood season, identify the pore water pressure, XY-displacement and stability safety factor at key points during the evolution process of seepage hazards of the levee during the ice flood season, and quantitatively evaluate the slope stability threshold of seepage hazards of the levee.

[0040] Compared with the prior art, the beneficial effects of the present invention are:

[0041] Aiming at the complex and changeable influencing factors of seepage hazards of the levee during the ice flood season, combining the actual water level change and frozen soil thickness during the ice flood season, by setting the combination of different variable rate flood processes and different thicknesses of frozen soil, simulate the evolution process of seepage hazards of the levee driven by the coupling of variable ice flood water level and frozen soil characteristics;

[0042] Through simulation calculation by the seepage analysis model of the levee, couple the seepage field-strain field, construct a seepage-stress strain field coupling model of the levee, and quantitatively analyze the changes of pore water pressure and XY-displacement inside the levee during the water level process.

[0043] By constructing a levee stability analysis model, study the theoretical relationship for calculating the slope stability threshold (safety factor) of seepage hazards of the levee during the ice flood season, and provide a theoretical reference for the disaster prevention of seepage hazards of the levee. Description of the Drawings

[0044] Figure 1 Flow chart of a method for simulating seepage danger of levee based on coupling of ice flood variable water level and frozen soil characteristics driven by the present invention;

[0045] Figure 2 Comparison chart of different variable water level process curves;

[0046] Figure 3 Schematic diagram of a simulation model for the evolution of seepage danger of levee during the ice flood period;

[0047] Figure 4 Variation curve of pore water pressure at monitoring points A1 to A6 at different stages;

[0048] Figure 5 Variation curve of pore water pressure at monitoring points B1 and B2 at different stages;

[0049] Figure 6 XY-displacement variation curve of monitoring point C1 during the rising and falling stages of water level;

[0050] Figure 7 Variation curve of the minimum safety factor of the levee slope with time and water level;

[0051] Figure 8 Comparison chart of the simulated value and the calculated value of the fitting formula of the safety factor of the levee slope. Specific implementation mode

[0052] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0053] As Figure 1 shown, a method for simulating seepage danger of levee based on coupling of ice flood variable water level and frozen soil characteristics driven by the present invention mainly includes the following processes:

[0054] S1, collection, processing and standardized compilation of basic data: Determine the research area, collect data on levee structure, hydrology, soil and frozen soil in the research area, mainly including cross-section dimensions, material parameters, and levee danger situations (phreatic line, slope displacement), river water level, frozen soil thickness and other index data, and perform preprocessing and standardized compilation to lay a data foundation for model construction and verification.

[0055] S2. Conduct regional ice flood variable water level and frozen soil characteristic analysis: To comprehensively evaluate the seepage danger of the levee, the ice flood variable water level and frozen soil thickness are coupled for seepage calculation and analysis of the levee, specifically including: Considering the characteristics of the rapid rise and fall of the ice flood water level, defining the variable water level characteristics, and setting the rapid changes in the water level simulated by the water level rising processes with various increasing rates and the water level falling processes with various decreasing rates as the variable water level characteristics. The simulated situations include sudden rise and fall of the water level, frequent water level fluctuations, a water level change gradient reaching or maintaining a high water level state for a long time; and, considering the obvious differences in frozen soil thickness in different periods and regions, setting multiple groups of equal-gradient frozen soil thicknesses in different periods and regions as the frozen soil characteristic rules, and representing the variation law of the seepage danger process of the levee under specific conditions through the combination method of "AND" of the current multiple water level rising / falling processes and multiple groups of equal-gradient frozen soil thicknesses, as the result of the regional ice flood variable water level and frozen soil characteristic analysis.

[0056] S3. Set up the simulation scenarios of the seepage danger of the levee during the ice flood period. Determine the simulated frozen soil thickness according to the result of the frozen soil characteristic analysis, and determine the simulated boundary conditions according to the result of the ice flood variable water level characteristic analysis, including hydraulic boundary conditions, stress boundary conditions, and strain boundary conditions: For example, determine the initial hydraulic boundary conditions according to the lowest water level, and take the water level 0.5 m above the design flood level as the highest flood level during the ice flood period. Set the backwater side of the levee as a constant water head, that is, the lowest water level; the water side of the levee is a function water head, that is, define the change process of the water head with time by inputting multiple groups of water level-time data. According to the historical water level change data of the river channel during the ice flood closing and opening periods, calculate the water level change rate by statistical methods, and use polynomial fitting for various variable rate water level change processes to simulate scenarios such as the rapid rise and sudden fall of the ice flood. Assume that the backwater side slope of the levee is an impermeable boundary. The stress boundary condition only considers the pore water pressure, and the strain boundary condition considers that the bottom of the levee foundation is a fixed boundary, there is no horizontal displacement on both sides of the levee foundation, and set appropriate sliding boundary conditions according to the water level change process for the possible slip surface and displacement direction.

[0057] S4. Build a simulation model for the seepage danger of the levee driven by the coupling of the variable water level and frozen soil characteristics during the ice flood period. Combine the basic data and the results of the ice flood variable water level and frozen soil characteristic analysis to determine the levee soil type and basic mechanical parameters (elastic modulus, internal friction angle, cohesion, Poisson's ratio, etc.), hydraulic parameters (saturated hydraulic conductivity, porosity, saturated soil water content, residual water content, etc.), input the levee cross-section dimensions, divide the cross-section network, set the material parameters and boundary conditions into the seepage danger simulation model of the levee, and realize the simulation analysis of the evolution process of the seepage danger of the levee; The construction of the seepage danger simulation model of the levee is based on basic theories such as the seepage analysis of the levee during the ice flood period, the deformation safety analysis and stability analysis of the coupling of the seepage field and strain field of the levee cross-section, specifically as follows:

[0058] 4.1, The basic theory of seepage analysis of the levee is as follows:

[0059] The expression of Darcy's law is:

[0060]

[0061] In the formula, v represents the average cross-sectional velocity, Q represents the flow rate of the cross-section, A represents the cross-sectional area, k represents the permeability coefficient, J represents the hydraulic gradient, H represents the total head, and s represents the length of the seepage path;

[0062] The expression of the general control differential equation for two-dimensional seepage is:

[0063]

[0064] In the formula, H represents the total head, k x , k y represent the permeability coefficients in the x and y directions, and θ represents the unit volume water content;

[0065] The seepage analysis model of the levee is obtained and solved by the finite element method. Based on Darcy's law and the water balance equation, the basic principle of groundwater flow is described. Among them, the control equation for two-dimensional saturated flow, the expression is:

[0066]

[0067] In the formula, m w represents the slope of the storage curve, γ w represents the unit weight of water; Q represents the increment or loss of water per unit volume, and the influence of Q is not considered;

[0068] 4.2, Establish a soil deformation safety analysis model for the coupling of the seepage field and strain field of the levee section: According to the simulated seepage danger evolution process of the levee seepage analysis model, ignoring other external forces, regarding the seepage force in the soil as the only external force affecting the deformation of the levee, analyzing the deformation mechanism of the levee driven by the coupling of the freezing-thawing variable water level and frozen soil characteristics, the flow equation and equilibrium equation of the soil, the expression is:

[0069]

[0070] In the formula, {F} represents the seepage force, {ε *} represents the virtual strain, σ * represents the virtual displacement, {Δσ} represents the internal stress, and T represents the transpose of the virtual strain vector and the virtual displacement vector;

[0071] The soil deformation safety analysis model for the coupling of the seepage field and strain field of the levee section is obtained, including:

[0072] 1) The element equilibrium equation for finite element coupling analysis, the expression is:

[0073] [K]{Δδ}+[L d {u w}={ΔF} (5)

[0074] In the formula, [K] represents the element stiffness matrix, {Δδ} represents the nodal displacement vector, [L d represents the seepage field - strain field coupling matrix of the levee section, {u w} represents the element pore water pressure vector; {ΔF} represents the external force increment vector acting on the element;

[0075] 2) Flow equation, the expression is:

[0076]

[0077] In the formula, β represents the coupling coefficient, describing the influence of soil deformation on seepage, [L f represents the seepage coupling matrix, Δt represents the time step, [K f represents the seepage hydraulic conductivity matrix, ω represents the relaxation coefficient, [M N represents the seepage mass matrix, {Δu w} represents the pore water pressure increment vector, {Q} |x+ΔM represents the external seepage at the position x + ΔM, {u w} |x represents the pore water pressure vector at the current position x;

[0078]

[0079]

[0080] In the formula, E represents the elastic modulus, v represents the Poisson's ratio, K B represents the bulk modulus, h represents the thickness of the soil layer for seepage analysis, R represents the seepage resistance coefficient;

[0081] 3) The expression of the two - dimensional section deformation finite - element equation is:

[0082] ∫ A [B] T [C][B]dA{α}=bt∫ A <n> T dA + pt∫ L <n> T dL (7)

[0083] where [C] represents the constitutive matrix, [B] represents the strain-displacement matrix, <n>Denote the interpolation function row vector, {α} denote the column vector, A denote the area of the element boundary, T denote the matrix transpose; L denote the element boundary length;

[0084] 4) The strain vector is defined by the engineering shear strain γ xy and the expression is:

[0085]

[0086] In the formula, ε x , ε y , ε z respectively denote the soil strains in the x, y, and z directions, and γ xy denotes the soil shear strain on the xy plane;

[0087] When ε z is 0, the expression of the corresponding two-dimensional plane strain matrix is:

[0088]

[0089] In the formula, N denotes the shape function matrix, which is used to interpolate the displacement at the nodes, and N i denotes the shape function of the i-th node. For an 8-node hexahedron element, N = {N 1 , N 2 , N 3 , …, N 8};

[0090] According to the elastic theory, the expression of the stress-strain relationship is:

[0091] {σ} = [C]{ε} (10)

[0092] In the formula, {σ} denotes the stress vector, {ε} denotes the strain vector, and [C] denotes the stiffness matrix;

[0093] 4.3. Based on the seepage field and seepage-stress-strain field coupling analysis model of the levee constructed in 4.2, a seepage stability analysis model of the levee driven by the coupling of variable water levels and frozen soil characteristics during the ice flood period is established: In the analysis of the stability of the levee, the limit equilibrium method is used to analyze the stress state of the slope when the levee fails. Based on the seepage-strain coupling finite element simulation of the present invention, the potential slip surface area is defined, the Morgenstern-Price method is adopted, and the semi-sine function is selected as the inter-slice force function to satisfy the moment balance and force balance. Through the iterative process, the ratio of the inter-slice shear force and the normal force is changed, and finally the safety factors of different potential slip surfaces are obtained. The minimum safety factor and the corresponding slip surface are concerned to evaluate and analyze the stability of the levee slope.

[0094] The expression of the stability safety factor of the levee slope is:

[0095]

[0096] Wherein, ∑T i represents the sum of shear stresses, Σ[cΔl i +(N i -u i Δl i )tanφ' e represents the sum of shear strengths, c represents the cohesion of the soil mass, N i , T i , u i , l i respectively represent the normal force, shear force, pore water pressure, and slip surface length on the i-th soil strip, and φ' e represents the effective internal friction angle of the soil mass.

[0097] The expression for the relationship between the shear force and normal force between soil strips is:

[0098] X = Eλf(x) (11)

[0099] Wherein, X represents the shear force between soil strips, E represents the normal force between soil strips, λ represents the proportionality factor under the action of the inter-strip force function f(x), which is an intermediate variable used to adjust the relationship between the inter-strip shear force and normal force, and f(x) represents the inter-strip force function;

[0100] Assuming that the points on the bottom shear plane of the soil strip are in the critical state of impending sliding, the expressions for the normal stress and shear stress at each point satisfying the Mohr-Coulomb criterion are:

[0101] ΔT = cΔx secα + (ΔN - uΔx secα)tanφ' e (12)

[0102] Wherein, T represents the shear force of the soil mass, N represents the normal force of the soil mass, c represents the cohesion of the soil mass, α represents the bottom inclination angle of the soil mass, u represents the pore water pressure, and φ' e represents the effective internal friction angle of the soil mass;

[0103] The present invention uses the finite element method to construct a levee structure model. According to the cross-section data of the river levee during the ice flood period, the geometric dimensions, hierarchical structure, and material properties of different layers of the levee are determined, including parameters such as the permeability coefficient, density, elastic modulus, and shear strength of the soil. An appropriate mesh type (such as quadrilateral mesh or triangular mesh) is used to mesh the entire cross-section for numerical simulation. Considering the differences in the levee structure and detailed material properties, the freezing condition of the levee soil is reflected by the frozen soil thickness and permeability coefficient in different periods (ice run period, river closure period, river opening period) and different regions during the ice flood period. And the method of optimizing the permeability coefficient of the frozen soil levee by region and layer is adopted, and the corresponding calculation parameters are assigned to the materials in different regions in combination with the on-site measured and investigated levee soil materials and frozen soil conditions.

[0104] S5. Simulate the evolution process of the seepage danger of the levee during the ice flood period:

[0105] 5.1. Simulation process of seepage calculation and analysis (evolution process) of the levee: Input the initial boundary conditions, simulate the seepage inside the levee under the initial lowest water level condition, and consider the pairwise combination of different ice flood variable water level processes and different frozen soil thicknesses according to the actual water level change process and frozen soil thickness during the ice flood period. Set various variable rate water level boundary conditions on the water-facing side of the levee, and calculate the distribution and change of water flow in the levee soil under different working conditions through seepage analysis.

[0106] 5.2. Simulation process of the stress and deformation conditions (evolution process) of the levee: Determine the stress and strain boundary conditions of the soil, and considering the influence of the pore water pressure of the water flow on the stress state of the levee, simulate the stress and deformation conditions of the soil under each working condition in combination with the calculation results of seepage analysis.

[0107] 5.3. Simulation process of the change in the slope stability of the levee: Analyze the possible slip surfaces inside the levee during the water level change process, and determine the positions and ranges of the entrances and exits of the slip surfaces. On the basis of seepage analysis and seepage-stress strain coupling analysis, combined with the limit equilibrium theory analysis, simulate and calculate the change process of the slope safety factor under different water levels and frozen soil conditions, and identify the key slip surface with the lowest safety factor and the potential instability region and seepage danger.

[0108] S6. Analyze the evolution law of the seepage danger of the levee during the ice flood period.

[0109] The embankment hazard indexes were selected to analyze the evolution law of embankment seepage hazard during the ice flood period. ① Since the pore water pressure is the pressure borne or transmitted by the pore water, it will cause the effective stress of the embankment soil to decrease. The area close to the waterside slope is usually the starting point of the seepage path. The head difference on this side is large, the seepage pressure is large, the seepage gradient is high, the change of pore water pressure is the most drastic, and the impact on the stability of the embankment is the most significant. Therefore, the key points in the area close to the waterside slope are selected to calculate the pore water pressure and analyze the change law of the pore water pressure of the embankment under different working conditions. ② Seepage may cause uneven settlement or lateral displacement in local areas of the embankment. The XY-displacement can fully reflect the deformation and stability of the embankment in the horizontal and vertical directions. Therefore, the XY-displacement of the key points is selected to reflect the influence of the ice flood variable water level coupled with frozen soil conditions on the embankment deformation. ③ The slope stability safety factor refers to the ratio of the anti-sliding force to the sliding force along the assumed sliding surface. By analyzing the change law of the embankment stability safety factor, the change of the embankment slope stability driven by the variable water level coupled with frozen soil characteristics can be studied. Therefore, in this simulation calculation, pore water pressure, XY-displacement and stability safety factor are mainly selected as calculation and analysis indicators. By quantitatively analyzing different indicators, the changing mechanism of embankment seepage driven by ice flood variable water level coupled with frozen soil characteristics is revealed.

[0110] The present invention is described in detail below through specific examples.

[0111] The present invention takes the typical dangerous sections of the dike in Ningxia of the Yellow River as the research object, takes into account the changes in the permeability of the dike soil after freezing during the ice flood period, and the influence of the variable water level conditions during the ice flood period on the evolution of the dike seepage, and conducts a dike seepage simulation study under the conditions of variable water level coupled with frozen soil during the ice flood period. By establishing a finite element numerical model, the evolution process of the dike seepage hazard in the Ningxia section of the Yellow River during the ice flood period is simulated and the evolution law of the hazard indicators is analyzed, which provides a certain reference basis for exploring the coupling mechanism of multiple factor changes on the dike seepage hazard and further revealing the mechanism of dike seepage change during the ice flood period.

[0112] Specific implementation steps:

[0113] Step 1: Basic data collection, processing and standardized compilation

[0114] The typical dangerous embankment sections of the Yellow River in Ningxia were identified as the research objects, and the embankment structure data, hydrological data, soil and frozen soil data of the typical dangerous embankment sections of the Yellow River in Ningxia were collected, including cross-sectional dimensions, material types, embankment hazards (seepage line, slope displacement), river water level and flow, soil and frozen soil mechanical parameters, frozen soil thickness, frozen soil distribution range and other indicator data. The data were pre-processed and standardized to lay a data foundation for the construction and verification of the embankment seepage hazard simulation model.

[0115] Step 2: Conduct analysis on the variable water levels during ice flood and frozen soil characteristics. The ice flood period in the Ningxia section of the Yellow River is caused by the sudden drop in winter temperature, which freezes the river water. When the temperature rises in spring, the ice and snow melt to form ice floes, leading to water level changes and seepage risks for the dikes. According to the analysis of the actual water level change data of the ice flood channel, during the river closure period, the river surface freezes, the water flow is blocked by the ice layer, and the water level tends to be stable, generally between 2 - 4m. During the river opening period, the temperature rises, the ice layer melts and rainfall increases, causing the water level to rise rapidly, usually rising 0.5 - 1.0m per day or even higher. When the ice in the river channel has basically melted, the water level reaches the highest value and the water level change tends to be stable, generally between 6.5 - 7.5m. Under ice floe dredging or high-temperature weather, the water volume is discharged from the river channel in a short time, and the water level drops rapidly, usually dropping 0.3 - 0.5m per day. The lowest water level reaches the lowest value between 3 - 4m. The sharp change in the water level during the ice flood period increases the seepage pressure of the dike soil mass and reduces the stability of the dike slope.

[0116] The formation and change of frozen soil in the dikes of the Ningxia section of the Yellow River are mainly affected by temperature, soil type, and water content. The thickness and scope of frozen soil directly affect the permeability and stability of the dikes. As the temperature drops, the dike soil mass gradually freezes, forming a stable frozen soil crust on the dike surface. At the initial stage of ice flood, the frozen soil thickness is usually between 0.3 - 0.5m. As the temperature drops, the thickness may further increase to more than 1m, and the maximum frozen soil thickness in some areas over the years can reach 1.6m. The formation of frozen soil changes the physical properties of the dike soil mass. The permeability coefficient of the frozen soil part of the same material is relatively small, resulting in a more complex seepage path and greatly increasing the risk of seepage failure of the dike.

[0117] Step 3: Set the simulation scenarios for seepage emergencies of dikes during ice flood period.

[0118] 1) Determine the boundary of variable water levels during ice flood. The lowest water level drops to the toe of the dike slope, which is 4m, and this is used as the initial boundary condition. The highest flood water level during ice flood is 0.5m above the design flood water level, that is, the relative water level elevation value is 8.5m. According to the historical water level change data of the river channel during the ice flood period of the Ningxia section of the Yellow River, the statistical method is used to calculate the water level change rate. Under the condition of reaching the same highest flood water level, the polynomial fitting method is used to set 3 kinds of ice flood water level rising processes with increasing change gradients, with durations of 4d, 4.5d, and 5d respectively. Set 3 kinds of ice flood water level dropping processes with decreasing change gradients, and the dropping durations are the same as those in the rising stage. The comparison of different variable water level process curves is as Figure 2 shown. Set different variable speed flood processes as the hydraulic boundary conditions on the water-facing side of the dike to simulate scenarios such as the rapid rise and sudden drop of ice flood.

[0119] 2) Determine the frozen soil thickness parameter. Based on the fact that seasonal frozen soil exists in the levees along the Ningxia section of the Yellow River in winter and the maximum frozen soil thickness in many years can reach 1.6 m, seven frozen soil thicknesses of 0 m (no frozen soil), 0.6 m, 0.8 m, 1.0 m, 1.2 m, 1.4 m, and 1.6 m are set. Since the filling layer and sandy loam layer are affected by freezing, the permeability coefficient of the frozen soil part of the same material is relatively small. Combine different variable water level processes with different frozen soil thicknesses in pairs to simulate the evolution process of levee seepage hazards under various scenario schemes.

[0120] Step 4, Construction of the levee seepage hazard simulation model during the ice flood period

[0121] According to the cross-section data of the river levees during the ice flood period in the Ningxia section of the Yellow River, determine the geometric dimensions and material parameters of the levees. The soil body of the typical levee dangerous section in the Ningxia section of the Yellow River can be divided into three layers. The levee body is mainly built with fill or loam, with a thickness of 5 m, and the main components are gravel, cobblestone mixed with sand. The levee foundation is mainly composed of a double-layer structure. The upper layer is a sandy loam layer, located under the filling, and the lower layer is a gravel layer with a large thickness and filled with coarse sand. In the present invention, the top width of the levee is set to 14 m, the height of the levee body is 5 m, the slope ratio is 1:2, the thickness of the upper sandy loam layer of the levee foundation is 2 m, and the thickness of the lower gravel layer of the levee foundation is 2 m. The entire levee cross-section is divided into 32,532 nodes and 32,018 elements, and the cell size is 0.1 m. According to the data such as the geological exploration report of the levee project in the Ningxia section of the Yellow River, determine the parameters such as the permeability coefficient of each layer of materials in the typical cross-section. Among them, the materials of the frozen soil layer consider the influence of soil freezing and have a small permeability coefficient. As shown in Table 1, it is the main parameter table of the levee soil material properties. Input the hydraulic boundary, stress boundary, and strain boundary conditions, and the structure of the levee seepage hazard simulation model during the ice flood period is as Figure 3 shown.

[0122] Table 1

[0123]

[0124] Step 5, Simulation of the evolution process of levee seepage hazards during the ice flood period

[0125] 1) Levee seepage evolution simulation. Assume that the backwater side slope of the levee is an impermeable boundary, input the initial boundary conditions, and simulate the seepage inside the levee under the condition of the initial lowest water level of 4.0 m. According to the actual water level change process and frozen soil thickness during the ice flood period, set a variable rate water level boundary condition on the water-facing side of the levee. Consider combining 3 ice flood variable water level processes with 7 frozen soil thicknesses in pairs to simulate the distribution and change of seepage in the levee soil under scenarios such as the sudden rise and sudden drop of the ice flood with different frozen soil thicknesses.

[0126] 2) Simulation of the evolution process of dike stress and deformation. Combining the calculation results of seepage analysis, it is determined that the bottom of the dike foundation is a fixed boundary, there is no horizontal displacement on both sides of the dike foundation, and only the influence of pore water pressure of the water flow on the stress state of the dike is considered to simulate the stress and deformation of the dike soil under various working conditions.

[0127] 3) Simulation of the change of dike slope stability. Analyze the possible slip surfaces inside the dike during the water level change process, determine that the slip surface appears on the backwater side during the water level rising stage and on the water-facing side during the water level falling stage, and draw the inlet and outlet ranges of the slip surface as 8m. Based on the seepage analysis and seepage-stress-strain coupling analysis, combined with the limit equilibrium theory analysis, simulate and calculate the change process of the slope safety factor under different water levels and frozen soil conditions, and identify the key slip surface with the lowest safety factor and the potential instability area and seepage danger.

[0128] Step 6, analysis of the evolution law of seepage danger of the dike during the ice flood period:

[0129] Taking the working condition with the rising and falling days of 5d and the frozen soil thickness of 1.2m as an example for analysis and explanation.

[0130] 1) Pore water pressure analysis

[0131] Since the pore water pressure near the water-facing slope changes first and significantly during the water level change process, a total of six monitoring points from A1 to A6 near the water-facing slope are selected for seepage analysis, and the positions of the monitoring points are as Figure 2 shown.

[0132] The curve of the change of pore water pressure at the monitoring points during the rising stage is as Figure 4 (a) shown. It can be seen that the faster the water level rises, the faster the pore water pressure increases. The lower the position of the monitoring point, the greater the pore water pressure. The response speeds of the pore water pressure of the monitoring points at the same height are different. The pore water pressures of the monitoring points A1, A3, and A5 near the water-facing slope change significantly first, followed by points A2, A4, and A6. Since water is resisted during the seepage process, the water head decreases and the pore water pressure decreases. Therefore, at the same height, the pore water pressure of the monitoring point near the water-facing side is slightly larger. And due to the smaller permeability coefficient inside the frozen soil layer, the head loss at the same distance increases, so the pore water pressure at point A2 is significantly less than that at point A1.

[0133] The curve of the change of pore water pressure at the monitoring points during the falling stage is as Figure 4 As shown in (b). As the water level drops, the pore water pressure at the monitoring point gradually decreases, and the faster the water level drops, the faster the pore water pressure decreases. During the process of water level drop, the change of pore water pressure at the monitoring point near the water-facing side at the same height is more significant. At the same moment, the pore water pressure at the monitoring point far from the water-facing side is relatively large. Since point A2 in the frozen soil layer is far from the water-facing side and the permeability inside the frozen soil layer is poor, the pore water pressure is difficult to release and initially remains at a relatively high level, and the comparison with the pore water pressure at point A1 is more obvious.

[0134] The influence of frozen soil factors on the pore water pressure near the toe of the backwater slope is relatively significant. Therefore, non-frozen part B1 and frozen soil internal B2 monitoring points are selected for analysis. The positions of the monitoring points are as Figure 2 shown. The curve graphs of the change of pore water pressure at the monitoring points in different stages are as Figure 5 shown.

[0135] During the water level rising stage, the pore water pressures at monitoring points B1 and B2 gradually increase. Since the permeability coefficient of the frozen soil part is small, the seepage resistance increases and the water head decreases. Therefore, the pore water pressure at B2 inside the frozen soil is smaller than that at B1 and the growth rate is slower. During the water level dropping stage, initially the pore water pressure at B1 is significantly larger than that at B2. During the process of water level drop, the pore water pressure at the monitoring points continuously decreases. Due to the poor permeability inside the frozen soil and the relatively small water flow penetration rate, the water cannot be discharged from the voids faster, and the decrease of the pore water pressure at monitoring point B2 is relatively slow.

[0136] 2) XY-Displacement Analysis

[0137] Since during the water level rising stage, the XY-displacement at the top of the backwater slope of the frozen soil levee is very sensitive to the change process of the water level, taking the monitoring point C1(32,9) at the top of the backwater slope as an example, the change situations during the water level rising and dropping stages are analyzed. The curve graphs of the XY-displacement change at the monitoring points during the water level rising and dropping stages are as Figure 6 shown. As Figure 6 can be seen, during the water level rising stage, the faster the rising speed, the faster the growth rate of the XY-displacement at point C1. This is because when the water level rises rapidly, the pore water pressure on the water-facing side increases rapidly, while on the backwater side, due to the permeability characteristics of the soil mass, the increase rate of the pore water pressure is relatively slow. This uneven pressure distribution will lead to the redistribution of the stress state inside the levee and cause the deformation of the soil mass.

[0138] At the beginning of the water level drop, the XY-displacement at point C1 suddenly increases. This is because the rapid drop of the water level leads to a rapid decrease in pore water pressure and a quick release, causing the soil to lose support, triggering a redistribution of internal stress in the levee, and thus resulting in rapid soil deformation and an increase in displacement. During the process of the water level drop, pore water drains outwards from the levee, and the soil will experience a certain degree of consolidation. The XY-displacement at point C1 first slightly decreases. Then, as the water level continues to drop, the pore water inside the levee continuously seeps out, the pore water pressure decreases, causing uneven settlement of the soil, and the XY-displacement at point C1 gradually increases.

[0139] 3) Minimum safety factor analysis

[0140] Select the slip surface where the minimum safety factor appears at the end of the water level change process, and obtain the curve of the minimum safety factor of the levee slope changing with time and water level as Figure 7 shown.

[0141] As can be seen from Figure 7 (a), during the water level rising stage, the safety factor K of the backwater slope gradually decreases as the water level rises. As the water level rises faster and faster, the hydrodynamic pressure acting on the backwater slope increases faster, resulting in a decrease in effective stress and a reduction in the shear strength of the soil, and the safety factor decreases rapidly. Initially, the hydrodynamic pressure acting on the water-facing slope is relatively small, and the safety factor remains basically unchanged. Later, as the water level continues to rise, the pore water pressure inside the water-facing slope increases, and the seepage pressure pointing towards the slope interior hinders the deformation and failure process of the water-facing slope, and the safety factor K increases somewhat.

[0142] During the water level drop stage, the safety factor K of the backwater slope gradually increases, and the safety factor K of the water-facing slope first decreases and then increases as the water level drops. Due to the sudden drop of the water level, the hydrodynamic pressure acting on the backwater slope decreases, and the stability increases. There is excess pore water pressure inside the water-facing slope, which is manifested as the hydrodynamic pressure for the levee to flow outwards, increasing the self-weight or sliding force of the levee, resulting in a reduction in slope stability. Later, as the water level drops more and more slowly, the water inside the levee continuously drains out, the seepage force acting on the water-facing slope continuously decreases, and the impact on stability also gradually becomes smaller, and the safety factor K continuously increases.

[0143] As can be seen from Figure 7 (b), when the rising height of the water level reaches 8.5 m, the safety factor of the backwater slope is the smallest, which is 0.95; when the water level drops to 5.9 m, the minimum value of the safety factor of the water-facing slope is 1.20. Considering that the seepage danger of the backwater slope of the levee is the greatest during the water level rising stage, based on the seepage simulation results, the relationship between the water level h and the safety factor K of the backwater slope during the rising stage is quantitatively studied. The simulation calculation results of seepage stability show that the relationship between the safety factor K and h can be expressed by a polynomial function, and the relationship formula is:

[0144] K 3 =0.1570+0.9075h-0.1386h 2 +0.0050h 3 #(13)

[0145] like Figure 8 As shown in the figure, the calculated values ​​and the actual simulated values ​​have a good overall fitting effect. After statistical analysis, the fitting correlation coefficient is 0.9959. Compared with the calculation results of the basic formula, it is proved to have a high reliability.

[0146] Considering the stage of water level decline, the safety factor of the waterside slope decreases first and then increases. There is a water level threshold that minimizes the safety factor K. Therefore, according to the simulation calculation results of seepage stability, the relationship between the water level h in the decline stage and the safety factor K of the waterside slope is quantitatively studied, which can be expressed by a polynomial function. The relationship is:

[0147] K 4 =2.3163-0.3663h+0.0307h 2 -7.5509*10 -5 h 3 #(14)

[0148] like Figure 8 As shown in the figure, the overall fitting effect between the calculated value of the formula and the actual simulation value is good. After statistical analysis, the fitting correlation coefficient is 0.9935. According to the fitted formula, when the water level drops to 6.089m, the safety factor reaches the minimum, and the water level change rate at this time is 0.05m / h. Compared with the calculation results of the basic formula, the relationship has a high reliability.

[0149] The above is a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered to fall within the scope of protection of the present invention.< / n> < / n> < / n> < / n> < / n> < / n>

Claims

1. A method for simulating embankment seepage hazards driven by ice flood variable water level coupled with frozen soil characteristics, characterized in that: include: S1, basic data collection, processing and standardized compilation; S2, based on the collected basic data, analyze the variable water level and frozen soil characteristics of the area to be simulated during the ice flood, including setting a combination of variable water level characteristics and frozen soil characteristics to represent the change process of levee seepage hazard, and obtaining the analysis results of variable water level and frozen soil characteristics during the ice flood period; S3, setting the scenario of embankment seepage hazard simulation during the ice flood period, determining the thickness of the simulated embankment frozen soil according to the analysis results of frozen soil characteristics, and determining the simulation boundary conditions according to the analysis results of the variable water level characteristics during the ice flood period, including hydraulic boundary conditions, stress boundary conditions and strain boundary conditions; S4, constructing a simulation model of levee seepage hazard driven by variable water level coupled with frozen soil characteristics during ice flood season, taking the cross-section size of the frozen soil levee, dividing the cross-section network, setting material mechanical parameters, hydraulic parameters and simulation boundary conditions as the input of the levee seepage hazard simulation model, combining basic data and the analysis results of variable water level and frozen soil characteristics during ice flood season to determine the levee soil type, basic mechanical parameters and hydraulic parameters, and using the levee slope stability safety factor to simulate and analyze the evolution process of levee seepage hazard; the construction of the levee seepage hazard simulation model specifically includes the following processes: 4.1, the governing equation of two-dimensional saturated flow is used as the dike seepage analysis model, and the expression is: In the formula, H represents the total water head, k x and k y represent the permeability coefficient in the x and y directions respectively, t represents time, m w represents the slope of the water storage curve, γ w It represents the specific gravity of water, Q represents the increase or loss of water per unit volume, and the influence of Q is not considered; The levee seepage analysis model is solved by the finite element method to describe the groundwater flow based on Darcy's law and water balance equation; 4.

2. Establish a soil deformation safety analysis model for the coupling of seepage field and strain field at the embankment section: According to the evolution process of embankment seepage danger simulated by the embankment seepage analysis model, the embankment deformation driven by the coupled frozen soil characteristics of ice flood and variable water level is analyzed, and the soil deformation safety analysis model for the coupling of seepage field and strain field at the embankment section is obtained, including: 1) The unit balance equation of finite element coupling analysis is expressed as: [K]{Δδ}+[L d ]{u w }={ΔF} Where [K] represents the element stiffness matrix, {Δδ} represents the node displacement vector, [L d ] represents the seepage field-strain field coupling matrix of the embankment section, {u w } represents the unit pore water pressure vector, and {ΔF} represents the external force increment vector acting on the unit; 2) The flow equation of finite element coupling analysis is expressed as: Where β is the coupling coefficient, which describes the effect of soil deformation on seepage, [L f ] represents the seepage coupling matrix, Δt represents the time step, [K f ] represents the seepage hydraulic conductivity matrix, ω represents the relaxation coefficient, [M N ] represents the seepage mass matrix, {Δu w } represents the pore water pressure increment vector, {Q} |x+ΔM represents the external seepage at position x+ΔM, {u w }| |x represents the pore water pressure vector at the current position x; In the formula, E represents the elastic modulus, v represents the Poisson's ratio, and K B represents the bulk modulus, h represents the soil thickness for seepage analysis, and R represents the seepage resistance coefficient; 3) The expression of the two-dimensional section deformation finite element equation is: ∫ A [B] T [C][B]dA{α}=bt∫ A <n> T dA+pt∫ L <n> T dL< / n> < / n> Where [C] represents the constitutive matrix, [B] represents the strain-displacement matrix, <n> represents the interpolation function row vector, {α} represents the interpolation function column vector, A represents the area of ​​the unit boundary, T represents the matrix transpose, and L represents the unit boundary length;< / n> 4) The expression of strain-displacement matrix is: Where N is the shape function matrix, which is used to interpolate the displacement at the nodes. i represents the shape function of the ith node. For an 8-node hexahedral element, N = {N1, N2, N3, …, N8}; Thus, the two-dimensional plane stress-strain relationship of the embankment structure is obtained; 4.

3. Based on the soil deformation safety analysis model of the seepage field-strain field coupling of the embankment section constructed in 4.2, a seepage stability analysis model of the embankment driven by the variable water level coupled with the frozen soil characteristics during the ice flood period is established: Based on the seepage-strain coupling finite element simulation, the potential slip surface area is defined, and the Morgenstern-Price method is used. The half-sine function is selected as the inter-strip force function to satisfy the moment balance and force balance. After an iterative process, the ratio of the inter-strip shear force and the normal force is changed, and finally the safety factor of different potential slip surfaces is obtained. The minimum safety factor and the corresponding sliding surface are evaluated and analyzed for the stability of the embankment slope. The expression of the embankment slope stability safety factor is: In the formula, ∑T i represents the sum of shear stress, Σ[cΔl i +(N i -u i Δl i )tanφ' e ] represents the sum of shear strength, c represents soil cohesion, N i , T i 、u i , l i denote the normal force, tangential force, pore water pressure, and slip surface length on the i-th soil strip, respectively, and φ' e It represents the effective internal friction angle of soil; S5, simulate the evolution of embankment seepage danger during ice flood season: 5.

1. Simulation process of levee seepage calculation and analysis: Input the initial boundary conditions, simulate the seepage inside the levee under the initial minimum water level condition, consider combining different ice flood water level change processes with different frozen soil thicknesses according to the actual water level change process and frozen soil thickness during the ice flood period, set a variety of variable rate water level boundary conditions on the water side of the levee, and calculate the distribution and change of water flow in the levee soil under different working conditions through seepage analysis; 5.

2. Simulation process of embankment stress and deformation: determine the stress and strain boundary conditions of the soil, combine the calculation results of seepage analysis, consider the influence of water pore water pressure on the stress state of the embankment, and simulate the stress and deformation of the soil under various working conditions; 5.

3. Simulation process of the change of embankment slope stability: Analyze the possible slip surface inside the embankment during the water level change process, and determine the location and range of the slip surface entrance and exit; Based on the seepage analysis and seepage-stress-strain coupling analysis, combined with the limit equilibrium theory analysis, simulate and calculate the change process of the slope safety factor under the coupling of variable water level and frozen soil characteristics, and identify the key slip surface with the lowest slope safety factor, as well as the potential instability area and seepage danger; S6, analyze the evolution law of embankment seepage danger during ice flood period: The embankment hazard indicators were selected to analyze the evolution law of the embankment seepage hazard during the ice flood period, to identify the pore water pressure, XY-displacement and stability safety factor of the key points in the evolution of the embankment seepage hazard during the ice flood period, and to quantitatively evaluate the slope stability threshold of the embankment seepage hazard.

2. The method for simulating embankment seepage danger conditions driven by ice flood variable water level coupled with frozen soil characteristics according to claim 1 is characterized in that: In step S1, the basic data at least include levee structure data, hydrological data, soil and frozen soil data in the study area; wherein the levee structure data at least include cross-sectional dimensions, material parameters, and indicator data including levee danger conditions represented by infiltration lines and slope displacements, river water levels, and frozen soil thickness.

3. The method for simulating embankment seepage danger conditions driven by ice flood variable water level coupled with frozen soil characteristics according to claim 1 is characterized in that: In the step S2, the initial hydraulic boundary conditions are determined according to the lowest water level, and the maximum flood level during the ice flood period is 0.5m above the design flood level; the backwater side of the levee is set to a constant head, that is, the lowest water level; the waterside of the levee is set to a function head, that is, the change process of the head over time is defined by inputting multiple sets of water level-time data; the water level change rate is calculated based on the historical water level change data of the river during the ice flood period, and a polynomial is used to fit a variety of variable rate water level change processes to simulate the rapid rise and sudden drop of ice floods; the slope on the backwater side of the levee is an impermeable boundary; the stress boundary condition considers the pore water pressure, and the strain boundary condition considers the bottom of the levee base as a fixed boundary, and appropriate sliding boundary conditions are set for possible slip surfaces and displacement directions according to the water level change process.

4. The method for simulating embankment seepage danger conditions driven by ice flood variable water level coupled with frozen soil characteristics according to claim 1 is characterized in that: 4.3 of step S4 further comprises: The relationship between the shear force and the normal force between soil strips is expressed as: X=Eλf(x) In the formula, X represents the shear force between soil strips, E represents the normal force between soil strips, λ represents the proportional factor under the action of the inter-strip force function f(x), which is an intermediate variable used to adjust the relationship between the inter-strip shear force and the normal force, and f(x) represents the inter-strip force function; The points on the bottom section of the soil strip are in a critical state of imminent sliding, and the normal stress and shear stress at each point satisfy the Mohr-Coulomb criterion, expressed as: ΔT=cΔxsecα+(ΔN-uΔxsecα)tanφ′ e In the formula, T represents the tangential force of the soil, N represents the normal force of the soil, c represents the cohesion of the soil, α represents the inclination angle of the bottom of the soil, u represents the pore water pressure, φ' e It represents the effective internal friction angle of soil.

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