Landslide sliding simulation method for real-time change of rock-soil mass parameters under rainfall infiltration

Abstract

The application discloses a landslide sliding simulation method for real-time change of rock-soil body parameters under rainfall infiltration, and comprises the following steps: a particle discrete element method (DEM) landslide model is established, rock-soil body parameters and boundary conditions are set, static force balance calculation is carried out to obtain an initial state of the landslide; grid division is carried out, seepage calculation grids are established, initial water content and seepage parameters in the fluid grids are valued, and the grids are grouped according to the particles; the boundary conditions of the landslide model are set to simulate rainfall infiltration, and the water content in the fluid grids is stored at a fixed time interval; the stored grid water content is called to modify the rock-soil body parameters in the grids in real time, and whether the landslide slides at the rainfall moment is calculated and obtained; if the landslide does not slide, the water content stored in the grids at the next moment is called to modify the rock-soil body parameters, and the landslide is re-solved and judged; if the landslide slides, additional solving calculation is carried out to obtain the movement of the landslide after sliding and the final accumulation form. The application realizes the simulation of the space-time change characteristics of the water content of the rock-soil landslide under the rainfall infiltration, realizes the simulation of the sliding duration of the landslide, the movement of the landslide after sliding and the final accumulation form after sliding under the rainfall, and overcomes the defects that the rock-soil body parameters are fixed and unchanged in the previous research on the rainfall infiltration landslide movement process.

Description

Technical Field

[0001] This invention relates to the field of numerical simulation of geological disasters, specifically a dynamic simulation method for landslides caused by the spatial and temporal changes in the water content of soil and rock under rainfall infiltration, which weakens the strength parameters of the soil and rock and increases the unit weight. In particular, it relates to a landslide simulation method for real-time changes in soil and rock parameters under rainfall infiltration. Background Technology

[0002] Numerous statistical data show that the vast majority of landslides occur during or after rainfall, and the degree of landslide development in a region tends to increase with the amount of rainfall. This indicates that rainfall is a significant factor in inducing landslide instability.

[0003] The adverse effects of rainfall infiltration on soil and rock landslides are mainly due to the changes in the water content of the slope caused by rainfall infiltration. This leads to a greater proportion of the soil and rock mass changing from an unsaturated state to a saturated state, resulting in increased density and decreased shear strength, thus causing landslide instability. Therefore, studying the impact of changes in soil and rock mass water content on landslide stability has significant scientific and engineering value.

[0004] Numerical simulation is an effective method for studying landslide stability. Currently, many scholars use finite element method (FE) software based on continuum mechanics theory to simulate and analyze the stability of landslides under rainfall. This method has achieved good simulation of the effects of rainfall duration and intensity on landslide stability. However, landslides are generally not continuous media, and the finite element method cannot simulate the movement characteristics and accumulation morphology of the soil and rock mass after a landslide. Therefore, methods based on discontinuous medium mechanics are introduced in landslide simulation. The discrete element method (DEM), as an effective method for studying the evolution of landslide movement, has received widespread attention from scholars for its ability to simulate the sliding process of the landslide body and the accumulation morphology of the deposited mass. However, simulating fluid dynamics is very difficult in the DEM.

[0005] How to simulate the sliding of landslide rock and soil under the influence of rainfall in discrete element method (DEM) calculations, and the motion characteristics and accumulation morphology of the landslide body after sliding, has become a technical problem that urgently needs to be solved in engineering. Summary of the Invention

[0006] Purpose of the invention: Addressing the limitations of the finite element method in simulating the motion characteristics and post-slide depositional morphology of landslides, and the lack of methods for simulating seepage calculations in the discrete element method, this invention proposes a landslide simulation method based on real-time changes in soil and rock parameters under rainfall infiltration. Using particle discrete element software, the method simulates the spatial and temporal changes in soil and rock moisture content caused by rainfall infiltration, leading to a decrease in soil and rock strength and an increase in density, thus inducing landslides. This method simulates the spatial and temporal changes in soil and rock moisture content under rainfall infiltration, and simulates the landslide duration, post-slide motion, and final depositional morphology considering real-time dynamic changes in soil and rock parameters under rainfall. This overcomes the shortcomings of previous studies that relied on fixed soil and rock parameters during rainfall-infiltrated landslides, making the numerical simulation consistent with actual engineering practices.

[0007] Technical solution: The present invention provides a method for simulating landslide sliding based on real-time changes in soil and rock parameters under rainfall infiltration, comprising the following steps:

[0008] (1) Based on the geological characteristics of the landslide, a particle discrete element DEM landslide model was established, and the parameters of the rock and soil mass and boundary conditions under the natural state were set. Static equilibrium calculations were performed to obtain the initial state of the landslide.

[0009] (2) The particle discrete element DEM landslide model is meshed, a seepage calculation mesh is established, the initial water content and permeability parameters of the fluid mesh are set, and the particles are grouped by mesh.

[0010] (3) Set fluid boundary conditions, iteratively solve the rainfall infiltration by calling the infiltration equation, obtain the water content in each fluid grid at each moment under the action of rainfall, and store the water content in the fluid grid at a fixed time interval.

[0011] (4) Modify the shear strength parameters and weight of the soil and rock by calling the stored grid moisture content, and perform static calculations during the rainfall period to determine whether the slope has slid during the rainfall period;

[0012] (5) If no sliding occurs, the stored next time grid water content is called to modify the soil and rock parameters and the judgment is made again; if sliding occurs, the calculation time is increased to obtain the motion state and final accumulation form after the landslide.

[0013] The soil and rock parameters in step (1) are obtained through indoor experiments. After the static equilibrium calculation, the velocity field and displacement field are cleared to zero to obtain the initial state of the landslide.

[0014] In step (2), the seepage calculation grid adopts the Euler coordinate system. The side length of the seepage calculation grid is determined according to the diameter of the particles in the established particle discrete element DEM landslide model. The number of grids in the horizontal and vertical directions in the seepage calculation grid is determined according to the size of the particle discrete element DEM landslide model.

[0015] In step (2), when the particles are grouped by grid, the particles in the same grid are grouped together, and each group of particles is a soil column. Then the entire discrete element DEM landslide model is composed of several soil columns.

[0016] In step (3), when iteratively solving the rainfall infiltration, the soil column is taken as the solution object, the grid is used as the basis, the fluid is taken as the continuous medium, and the water content in each grid at different times is solved iteratively by calling the infiltration equation.

[0017] In step (3), the fluid boundary condition is the rainfall intensity, the expression for which is shown in equation (1), and the discretization scheme for which is shown in equation (2). The infiltration equation used is Richards' vertical infiltration equation for rainfall, as shown in equation (3), and the discretization scheme for Richards' vertical infiltration equation for rainfall is shown in equation (4).

[0018]

[0019]

[0020]

[0021]

[0022] D(θ) is the diffusivity; θ is the water content; k(θ) is the permeability coefficient when the water content is θ; Δy is the length of the grid in the y direction; q is the rainfall intensity; and Δt is the time step.

[0023] In step (3), the fluid boundary condition is the rainfall intensity. When performing rainfall infiltration calculation, the conversion between the iteration step and the actual time is achieved by setting the time step Δt.

[0024] In step (3), the VG model is used to determine the relationship between D, k and water content in the infiltration equation, as shown in equations (5) to (8):

[0025]

[0026] k(θ)=k s (1+β)- 2.5m ((1+β) m -β m ) 2 (6)

[0027]

[0028]

[0029] In the formula: D(θ) is the diffusivity; C(θ) is the water content; θ is the water content; s θ is the saturated water content; θ0 is the residual water content; k(θ) is the permeability coefficient when the water content is θ; k s Saturated permeability coefficient; h a , n, m are the coefficients of the VG model, which were determined experimentally.

[0030] In step (3), the water content in the fluid grid at different times is called to obtain the relationship between water content and depth at a certain time.

[0031] In step (4), the shear strength parameters of the soil and rock mass and the weight of the soil are assigned by mobilizing the grid moisture content stored in step (3). The relationship between moisture content and shear strength of soil and rock mass and weight of soil is obtained through indoor experiments.

[0032] In step (4), after modifying the shear strength parameters and weight of the soil and rock mass according to the stored grid moisture content, the static solution calculation time during the rainfall period is consistent with the rainfall infiltration time under the same moisture content in step (3), thereby realizing the simulation of whether the slope slides during the actual rainfall duration.

[0033] In step (5), two termination conditions are set. One is that after calling the last stored moisture content, the landslide does not slide during the static solution, indicating that the landslide does not slide during the rainfall period. The other is that when the stored moisture content is called, the landslide slides during the static solution, indicating that the landslide slides at this point in the rainfall.

[0034] If the termination condition in step (5) is of the second type, a certain amount of calculation time is added to obtain the movement process and accumulation pattern of the landslide after sliding.

[0035] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0036] (1) This invention realizes the simulation of the spatial and temporal variation of water content of landslide soil under rainfall infiltration by dividing the mesh in particle discrete element software.

[0037] (2) The present invention divides the soil and rock mass into several soil columns by grouping the soil and rock mass into grids, and uses the soil columns as the solution object when solving the seepage, thus reducing the amount of calculation.

[0038] (3) By calling the water content in the fluid grid, the present invention realizes the coupling between fluid and solid, solves the problem that it is difficult to consider the influence of rainfall infiltration in the process of simulating the movement of landslides under rainfall in the particle discrete element simulation of the prior art, and realizes the simulation of the change of water content in the landslide under rainfall, the duration of landslide sliding, the movement state of the landslide after sliding and the deposition morphology after sliding. Attached Figure Description

[0039] Figure 1 This is a flowchart of the landslide sliding simulation method based on the real-time changes of soil and rock parameters under rainfall infiltration.

[0040] Figure 2 This is a diagram of the discrete element DEM landslide calculation model established in this embodiment of the invention;

[0041] Figure 3 This refers to the fluid computational grid in this embodiment of the invention;

[0042] Figure 4 This is a soil column diagram after the landslide particles are grouped in an embodiment of the present invention;

[0043] Figure 5 This is a graph showing the change in soil moisture content with depth at different times in an embodiment of the present invention;

[0044] Figure 6 Displacement diagram of landslide particles during a rainfall duration of 0.3 hours in an embodiment of the present invention;

[0045] Figure 7 This is a graph showing the change in particle displacement at the upper right corner of the landslide over time after the landslide occurred.

[0046] Figure 8 This is a graph showing the change in particle velocity over time in the upper right corner of the landslide after the landslide occurred.

[0047] Figure 9 This is a diagram showing the accumulation pattern after the landslide instability and sliding in the example. Detailed Implementation

[0048] like Figure 1 As shown, the landslide sliding simulation method based on real-time changes in soil and rock parameters under rainfall infiltration of the present invention includes the following steps:

[0049] (1) Based on the geological characteristics of the landslide, a particle discrete element DEM landslide model was established, and the parameters of the rock and soil mass and boundary conditions under the natural state were set. Static equilibrium calculations were performed to obtain the initial state of the landslide.

[0050] (2) Mesh the particle discrete element DEM landslide model, establish a seepage calculation grid, set the initial water content and permeability parameters of the fluid grid, and group the particles through the grid;

[0051] (3) Set fluid boundary conditions, call the infiltration equation to iteratively solve the rainfall infiltration, obtain the water content in each fluid grid at each moment under the action of rainfall, and set a fixed time interval to store the water content in the fluid grid;

[0052] (4) Modify the shear strength parameters and weight of the soil and rock by calling the stored grid moisture content, and perform static calculations during the rainfall period to determine whether the landslide will occur during this rainfall period.

[0053] (5) If no sliding occurs, the stored next time grid water content is called to modify the soil and rock parameters and make another judgment; if sliding occurs, the calculation time is increased to obtain the motion state and accumulation shape of the landslide after sliding.

[0054] In step (1), the parameters of the soil and rock mass are obtained through indoor experiments. Based on the experimental results, the mechanical parameters of the soil and rock mass are calibrated and set. These mechanical parameters include tensile strength, shear strength, friction coefficient, normal and shear stiffness. At the same time, the boundary conditions of the landslide model are set as fixed boundaries. After static solution, the velocity field and displacement field are cleared to zero.

[0055] In step (2), the fluid grid uses the Euler coordinate system. The side length of the seepage calculation grid is determined according to the diameter of the particles in the established discrete element DEM landslide model. The number of grid cells in the horizontal and vertical directions in the seepage calculation grid is determined according to the size of the particle discrete element DEM landslide model.

[0056] In step (2), the particles are grouped by grid. The horizontal direction is taken as the horizontal axis. Particles in the same grid with the same horizontal coordinate are grouped together, and each group of particles is given a different group name. Each group of particles is a soil column.

[0057] In step (3), when iteratively solving for rainfall infiltration, rainfall intensity is used as the boundary condition, the grid is used as the basis, the fluid is used as the continuous medium, and the soil column is used as the solution object. The infiltration equation is called to iteratively solve for the water content at different depths of the soil column. The solution is performed on one soil column, and then it represents the other soil columns. The expression for rainfall intensity as the boundary is shown in equation (1), and the discretization format is shown in equation (2). The infiltration equation used is the Richards rainfall vertical infiltration equation, as shown in equation (3), and the discretization format is shown in equation (4).

[0058]

[0059]

[0060]

[0061]

[0062] D(θ) is the diffusivity; θ is the water content; k(θ) is the permeability coefficient when the water content is θ; Δy is the length of the grid in the y direction; q is the rainfall intensity; and Δt is the time step.

[0063] In step (3), when solving for rainfall infiltration, Δt represents the rainfall time represented by one iteration. The product of Δt and the iteration step is the actual rainfall time. A fixed time interval is set to store the water content in the fluid grid during the seepage calculation.

[0064] In the infiltration equation, the VG model is used to determine the relationship between D, k and water content, and the specific expressions are shown in equations (5) to (8):

[0065]

[0066] k(θ)=k s (1+β)- 2.5m ((1+β) m -β m ) 2 (6)

[0067]

[0068]

[0069] In the formula: D(θ) is the diffusivity; C(θ) is the water content; θ is the water content; s θ is the saturated water content; θ0 is the residual water content; k(θ) is the permeability coefficient when the water content is θ; k s Saturated permeability coefficient; h a , n, m are the coefficients of the VG model.

[0070] By calling the grid moisture content stored at different times, the relationship between moisture content and depth at a certain time can be obtained.

[0071] In step (4), the shear strength parameters of the soil and rock mass and the weight of the soil are assigned by adjusting the water content stored in step (3). The specific relationship between the water content and the shear strength and weight of the soil and rock mass is obtained through indoor experiments.

[0072] In step (4), the time for statically solving the landslide based on the modified shear strength and unit weight of the soil and rock is consistent with the time for rain infiltration when the water content decreases in step (3), so as to simulate whether the landslide will slide under the actual rainfall duration.

[0073] In step (5), two termination conditions are set. One is that after calling the last stored moisture content, the landslide does not slide during the static solution, indicating that no landslide occurs during that rainfall duration. The other is that when the stored moisture content at a certain moment is called, the landslide slides during the static solution, indicating that the landslide occurred at that moment, and the subsequent calls for moisture content are terminated. In step (5), if the termination condition is the second type, a certain amount of calculation time is added to obtain the movement process and final deposition morphology of the landslide after sliding.

[0074] Example

[0075] Taking the instability of a homogeneous soil landslide under rainfall as an example, the simulation method for the instability process of a soil landslide under rainfall according to the present invention will be described in detail.

[0076] 1. Based on the geological conditions of the landslide, a particle discrete element (DEM) landslide model was established, with a particle diameter of 0.05 m. Natural soil and rock parameters and boundary conditions were set. After static equilibrium calculations, the velocity and displacement fields were zeroed to obtain the initial state of the landslide. The landslide model is as follows: Figure 2 As shown.

[0077] 2. The landslide is meshed according to particle size to establish a seepage calculation grid. In this case, the grid cells are square with a side length equal to the particle diameter of 0.05m. The resulting fluid calculation grid is shown below. Figure 3 As shown. The particles are grouped according to their x-coordinate in the same grid, and each group is considered a soil column. The entire landslide then consists of several soil columns. The landslide model after grouping is shown below. Figure 4 As shown.

[0078] 3. Using rainfall intensity as the boundary condition, the rainfall intensity q = 1 / (3.6e4) m / s is set. The rainfall infiltration boundary condition is set by equation (9). By calling the infiltration equation (10), any soil column is selected for rainfall infiltration iteration solution. The relationship between D and K in the infiltration equation and water content is determined by the VG model. The specific expressions and parameter values ​​are shown in equations (11) to (14). The time step Δt = 2 is set. The water content in the soil column grid is stored once every 180 iterations. The actual storage time interval is 0.1h. In this case, the landslide water content change situation is stored for 3 hours. By calling the stored water content, the water content change with depth is obtained, as shown in equation (11) to (14). Figure 5 As shown.

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085] 4. The stored moisture content values ​​are retrieved sequentially. The relationship between moisture content and the shear strength and unit weight of the soil and rock mass is determined through indoor experiments. In this case, the tensile strength, shear strength, and unit weight change with the moisture content, as shown in equations (14) to (7). After modifying the soil and rock mass parameters, a static solution is performed to determine whether the slope has slid during this rainfall period. Figure 6 The data shows the displacement of the landslide after 0.3 hours of rainfall, indicating that the landslide had not yet occurred at this time.

[0086] ten=ten0(1-0.7(θ-θ1) / (θ s -θ1)=20(1-0.7(θ-0.15) / (0.5-0.15)(14)

[0087] she=she0(1-0.7(θ-θ1) / (θ s -θ1)=30(1-0.7(θ-0.15) / (0.5-0.15)(16)

[0088] γ=9.8ρ0(1+θ-θ1)=9.8*1500(1+θ-0.15)(17)

[0089] The system continues to use the stored moisture content from the next time step to modify the shear strength and unit weight of the soil and rock mass. When the 11th stored moisture content is used, the landslide occurs, indicating that the landslide occurred after 1.1 hours of rainfall. Since the storage time interval in this case is 0.1 hours, no additional calculation time is needed to obtain the motion state and deposition morphology of the landslide mass after the landslide. Figure 7 This is a graph showing the displacement of particles in the upper right corner of the landslide over time after the landslide occurred. Figure 8 This is a graph showing the change in particle velocity over time in the upper right corner of the landslide after the landslide occurred. Figure 9 This is a diagram showing the depositional morphology after a landslide.

Claims

1. A landslide sliding simulation method based on real-time changes in soil and rock parameters under rainfall infiltration, characterized in that: Includes the following steps: (1) Based on the geological characteristics of the landslide, a particle discrete element DEM landslide model was established, and the parameters of the rock and soil mass and boundary conditions under the natural state were set. Static equilibrium calculations were performed to obtain the initial state of the landslide. (2) Mesh the particle discrete element DEM landslide model, establish a seepage calculation grid, set the initial water content and permeability parameters of the fluid grid, and group the particles by grid; (3) Set fluid boundary conditions, call the infiltration equation to iteratively solve the rainfall infiltration, obtain the water content in each fluid grid at each time under rainfall, and store the water content in the fluid grid at a fixed time interval; the fluid boundary condition is the rainfall intensity, which is determined by adjusting the time step during the rainfall infiltration calculation. The settings allow for the conversion between iteration steps and real time. The expression for rainfall intensity is shown in Equation (1), and the discrete format of rainfall intensity is shown in Equation (2); the infiltration equation adopted is the Richards vertical infiltration equation for rainfall, as shown in Equation (3), and the discrete format of the Richards vertical infiltration equation for rainfall is shown in Equation (4): （1） （2） （3） （4） In the formula: The diffusivity; Moisture content; The moisture content is Permeability coefficient at that time The length of the grid in the y-direction; Rainfall intensity, For time steps; (4) Modify the shear strength parameters and weight of the soil and rock by calling the stored grid moisture content, and perform static calculations during the rainfall period to determine whether the landslide has occurred during the rainfall period; (5) If no slip occurs, the stored next time grid water content is used to modify the soil and rock parameters, and the judgment is made again; If a landslide occurs, the calculation time is increased to obtain the motion state and accumulation pattern after the landslide.

2. The landslide sliding simulation method based on real-time changes in soil and rock parameters under rainfall infiltration as described in claim 1, characterized in that: In step (1), after performing static equilibrium calculations, the velocity field and displacement field of the particle discrete element DEM landslide model are cleared to zero to obtain the initial state of the landslide.

3. The landslide sliding simulation method based on real-time changes in soil and rock parameters under rainfall infiltration as described in claim 1, characterized in that: In step (2), the seepage calculation grid adopts the Euler coordinate system. The side length of the seepage calculation grid is determined according to the diameter of the particles in the established discrete element DEM landslide model. The number of grids in the horizontal and vertical directions in the seepage calculation grid is determined according to the size of the particle discrete element DEM landslide model.

4. The landslide sliding simulation method based on real-time changes in soil and rock parameters under rainfall infiltration as described in claim 1, characterized in that: In step (2), when grouping particles by grid, particles in the same grid with the same horizontal coordinate are grouped into one group, and each group of particles is a soil column.

5. The landslide sliding simulation method based on real-time changes in soil and rock parameters under rainfall infiltration as described in claim 4, characterized in that: In step (3), when iteratively solving the rainfall infiltration, the soil column is taken as the solution object, the grid is used as the basis, the fluid is taken as the continuous medium, and the water content in each grid at different times is solved iteratively by calling the infiltration equation.

6. The landslide sliding simulation method based on real-time changes in soil and rock parameters under rainfall infiltration as described in claim 1, characterized in that: In step (3), the VG model is used to determine the relationship between D, k and water content in the infiltration equation. The relationship expressions are shown in equations (5) to (8): （5） （6） （7） （8） In the formula: The diffusivity; Water holding capacity; Moisture content; This represents the saturated moisture content. Residual moisture content; The moisture content is Permeability coefficient; The saturated permeability coefficient; , , These are the coefficients of the VG model.

7. The landslide sliding simulation method based on real-time changes in soil and rock parameters under rainfall infiltration as described in claim 1, characterized in that: In step (3), the water content in the fluid grid at different times is called to obtain the relationship between water content and depth at a certain time.

8. The landslide sliding simulation method based on real-time changes in soil and rock parameters under rainfall infiltration as described in claim 1, characterized in that: In step (4), after modifying the shear strength parameters and weight of the soil and rock mass according to the stored grid moisture content, the static solution calculation time during the rainfall time is consistent with the rainfall infiltration time under the moisture content described in step (3), thereby simulating whether the landslide will slide during actual rainfall.

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