Variable terrain landslide surge simulation method based on DEM and water wave model

Abstract

The invention discloses a variable terrain landslide surge simulation method based on a DEM (Digital Elevation Model) and a water wave model. The method comprises the following steps: (1) establishing a landslide motion calculation model by using a DEM method; (2) carrying out landslide motion numerical simulation by using the landslide motion calculation model, and extracting information of all spherical particles forming a landslide body in the calculation process; (3) constructing a surge evolution calculation model by using a water wave model, and extracting node coordinates in the surge evolution calculation model as initial terrain node coordinates; (4) reconstructing the terrain of the surge evolution calculation model according to the motion characteristics of the landslide mass, and further establishing the terrain changing along with the motion of the landslide mass; (5) introducing a terrain which changes along with the movement of the landslide mass into the surge evolution calculation model, and carrying out surge evolution numerical simulation; and (6) verifying the effectiveness of the surge evolution calculation model by using a physical model test. The problem that landslide movement and accumulation are difficult to consider in a water wave model is solved, and a way is provided for landslide surge numerical simulation.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for simulating landslide sliding process in the field of landslide surge research, and particularly relates to a variable-terrain landslide surge simulation method based on DEM and water wave model. BACKGROUND

[0002] During the operation of a reservoir in a mountainous area, landslide surge induced by slope instability on the reservoir bank is an important factor threatening the safety of the reservoir area. After the generation of landslide surge in a mountainous reservoir, the energy of the surge is slowly dissipated due to the influence of the narrow river channel. The surge carrying huge energy often propagates along the river channel for several kilometers or even tens of kilometers, resulting in a wide disaster range, and the entire landslide surge disaster chain spans different time and space scales. With the continuous development of hydropower development towards the southwest mountainous area, the demand for landslide surge disaster assessment of mountainous reservoirs is increasing.

[0003] Landslide surge mainly includes the following processes: landslide instability and sliding, accumulation in the river channel, surge generation, propagation along the river channel, climbing, overtopping or reflecting on the dam surface, and finally subsiding. It is a complex chain of geological disasters. Numerical simulation is an important means to study landslide surge disasters. Through the coupling calculation of different methods, the dynamic evolution process of landslide and landslide surge can be accurately reflected.

[0004] At present, DEM-CFD, DEM-SPH, DDA-SPH, PD-SPH and other coupling methods have been applied in landslide surge research and have achieved good results. However, most of the coupling models require large computational resources, resulting in the calculation range being concentrated in the vicinity of the landslide body.

[0005] For the problem of surge propagation involving a wide area, a depth-integrated water wave model is usually used for solution. In the application of the water wave model, a key problem is how to accurately input the initial surge generated by the landslide into the water: existing methods either determine the initial surge by an empirical formula and input it into the water wave model, or calculate the characteristics of the initial surge by a main profile model and input the initial surge waveform at the surge generation boundary. However, these methods ignore the movement and accumulation characteristics of the landslide body, and the calculation results may have certain deviations.

[0006] How to use a variable-terrain landslide surge simulation method and effectively consider the complex movement characteristics of the landslide body in the water wave model to provide an effective way for solving the landslide surge problem is a technical problem that needs to be solved. SUMMARY

[0007] Invention purposes: In view of the deficiencies in the prior art, the present application provides a variable terrain landslide surge simulation method based on DEM and water wave model. The DEM method is used to establish a landslide movement calculation model, and a terrain that changes synchronously with the landslide movement is constructed in the water wave model. Based on the terrain change, the surge evolution simulation is carried out, which solves the problem of difficult consideration of complex movement and accumulation of landslide in the water wave model, and finely captures the landslide movement process, providing a beneficial approach for rapid and accurate landslide surge simulation analysis.

[0008] Technical scheme: The variable terrain landslide surge simulation method based on DEM and water wave model of the present application comprises the following steps:

[0009] (1) A DEM method is used to establish a landslide movement calculation model with the center of the landslide body as the center. The process is as follows: a three-dimensional sliding surface of the landslide body is established from the sliding surface of the profile of the landslide body and the landslide limit at the original ground surface; after the closed space formed by the sliding surface of the landslide body and the original ground surface is discretized by spherical particles, the surface of the landslide body in the original ground surface is deleted, and the sliding surface of the landslide body is connected with the original ground surface to form the bottom boundary of the landslide sliding; after the bottom boundary is fixed, the bottom boundary is discretized by Wall unit;

[0010] (2) The landslide movement numerical simulation is carried out by using the landslide movement calculation model until the landslide body stops moving, and the X, Y, Z coordinates and radius of the center of each spherical particle constituting the landslide body are extracted;

[0011] (3) According to the river terrain and the sliding surface of the landslide body, a surge evolution calculation model is constructed by using a water wave model, and the node coordinates in the surge evolution calculation model are extracted as the initial terrain node coordinates; the river boundary is set as an open boundary, and the X, Y and Z coordinates of each node are extracted by traversing each node of the surge evolution calculation model;

[0012] (4) According to the X, Y, Z coordinates and radius of the center of each spherical particle in the landslide movement numerical simulation in step (2), the terrain of the surge evolution calculation model is reconstructed, and the terrain that changes with the movement of the landslide body is established;

[0013] (5) On the basis of the surge evolution calculation model, the terrain that changes with the movement of the landslide body is introduced into the water wave model for surge evolution numerical simulation, and time iteration calculation is carried out, and the maximum wave height at the thalweg of the surge evolution calculation model is extracted;

[0014] (6) A landslide surge large-scale physical similarity model test is carried out and the maximum wave height of the measuring point is obtained, and the maximum wave height of the measuring point is compared with the maximum wave height of the corresponding position in the surge evolution calculation model in step (5), to verify the accuracy of the calculation result in step (5).

[0015] In step (1), the discrete process of the closed space formed by the sliding surface in the landslide body and the ground surface is as follows: first, the particle size interval of the ball particle is determined, then the ball particle of a given particle size interval is filled in a region covering the space where the landslide body is located until the porosity of the space reaches the set porosity; the ball particles outside the space where the landslide body is located are deleted, and finally the initial equilibrium of the ball particles inside the space where the landslide body is located is performed to form a contact ball particle cluster.

[0016] In step (4), the steps of reconstructing the terrain of the surge evolution calculation model are as follows:

[0017] (4.1) Search for the X and Y coordinates of the initial terrain node of the water wave model in the vertical projection region of a single ball particle, calculate the elevation h of the upper surface of the ball particle relative to the X and Y coordinates, and the calculation formula is:

[0018] In the formula: is the elevation of the upper surface of the ball particle relative to the X and Y coordinates; is the X coordinate of the ball center, is the Y coordinate of the ball center, is the Z coordinate of the ball center; R is the radius of the ball particle; is the X and Y coordinates of the initial terrain node of the water wave model in the vertical projection region of the ball particle;

[0019] If the elevation of the upper surface of the ball particle relative to the X and Y coordinates is higher than the Z coordinate elevation of the initial terrain node at the X and Y coordinates, the Z coordinate elevation of the initial terrain node at the X and Y coordinates is updated using the elevation of the upper surface of the ball particle relative to the X and Y coordinates, otherwise the Z coordinate elevation of the terrain node is kept unchanged;

[0020] (4.2) Repeat steps (4.1) to traverse all ball particles, and if the elevation of the initial terrain node has been updated, use the updated terrain node elevation for comparison;

[0021] (4.3) Steps (4.1) and (4.2) are performed at each terrain change time of the landslide movement calculation model to construct the terrain of the surge evolution calculation model corresponding to the current time landslide movement; at the beginning of each update time, the initial terrain of the surge evolution calculation model is used as the basis to integrate the reconstructed terrain of the surge evolution calculation model at each time to form the terrain of the surge evolution calculation model that changes with the landslide movement;

[0022] (4.4) After the landslide stops moving, the terrain of the surge evolution calculation model remains unchanged.

[0023] ​In step (1), after fixing the bottom boundary, the bottom boundary is discretized by Wall elements, and the side length of the Wall elements is greater than the particle size of the spherical particles.

[0024] In step (1), the sliding surface of each profile is determined according to the engineering geological profile of the landslide body.

[0025] In step (2), the process of numerical simulation of landslide movement by using the landslide movement calculation model is as follows:

[0026] (2.1) The parallel bond model is used to represent the strength characteristics and deformation characteristics of the rock-soil mass, and the linear elastic model is used to represent the friction coefficient of the landslide body with the sliding surface during the sliding process;

[0027] (2.2) The gravity, buoyancy and drag force are applied to the landslide body in the landslide movement calculation model to simulate the landslide movement, and the process of the landslide body sliding and disintegrating, sliding into the river and accumulating in the river is obtained.

[0028] In step (2.2), the drag force acts on the submerged spherical particles, and the direction is opposite to the direction of the motion of the spherical particles, and the calculation formula of the drag force is as follows:

[0029] wherein, is the comprehensive drag coefficient; is the density of water; is the cross-sectional area of the spherical particle; is the sliding speed of the spherical particle.

[0030] In step (2.2), the buoyancy received by the landslide body during the water entry process is calculated by the volume of the water displaced, and the volume of the water displaced by the completely submerged spherical particles is equal to the volume of the spherical particles themselves; the volume of the water displaced by the partially submerged spherical particles is calculated according to the volume of the spherical particles below the water surface.

[0031] In step (3), the initial terrain of the surge evolution calculation model is the original terrain of the river, and the terrain at the landslide body is the sliding surface of the landslide body.

[0032] Preferably, in step (4.1), before reconstructing the terrain of the water wave model, the initial terrain node range required to be searched in the water wave model is determined based on the modeling range of the landslide movement calculation model, so as to avoid searching all the terrain nodes in the water wave model and causing calculation redundancy.

[0033] Further, in step (4.1), during the node searching process for each spherical particle, the K-D Tree method is used to improve the searching efficiency.

[0034] In step (5), when the landslide surge calculation is performed in the water wave model, the terrain varying with the landslide movement is introduced, and the water level at the corresponding position is changed to maintain the mass conservation under the influence of the terrain change, thereby driving the fluid movement. With the continuous change of the terrain, the water level is also constantly changed, thereby generating the surge in the surge evolution calculation model and realizing the simulation of the surge evolution process.

[0035] In step (6), the verification method is to verify the effectiveness of the surge evolution calculation model by comparing the maximum wave height distribution of the surge evolution calculation model and the large-scale physical similar model of the landslide surge.

[0036] Advantages: Compared with the prior art, the present application has the following advantages:

[0037] (1) The landslide surge simulation method based on DEM and water wave model of variable terrain of the present application adopts the DEM method to establish a landslide movement calculation model, considers the buoyancy and drag force of the water body on the landslide movement, and can finely capture the landslide movement evolution process.

[0038] (2) The landslide surge simulation method of the present application extracts the landslide movement characteristics, constructs the terrain varying synchronously with the landslide movement in the water wave model, and carries out the surge evolution simulation based on the terrain change, thereby providing a reliable technical approach for carrying out the numerical simulation of the landslide surge. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The flow chart of the landslide surge simulation method based on DEM and water wave model of variable terrain of the present application;

[0040] Figure 2 The landslide movement calculation model established in the embodiment of the present application;

[0041] Figure 3 The landslide movement process obtained by the landslide movement calculation model in the embodiment of the present application;

[0042] Figure 4 The surge evolution calculation model constructed using the water wave model in the embodiment of the present application;

[0043] Figure 5 The terrain reconstruction of the surge evolution calculation model at a typical moment in the embodiment of the present application;

[0044] In the embodiment of the present application, Figure 5 (a) is the landslide movement characteristics at a typical moment in the embodiment of the present application;

[0045] Figure 5 (b) is the terrain reconstruction of the surge evolution calculation model at a typical moment in the embodiment of the present application;

[0046] Figure 6 The surge evolution process obtained in the embodiment of the present application;

[0047] Figure 7 The verification situation of the surge evolution calculation model in the embodiment of the present application. DETAILED DESCRIPTION

[0048] As Figure 1 shown, the variable-terrain landslide surge simulation method based on DEM and water wave model of the present application comprises the following steps:

[0049] (1) A DEM method is adopted to establish a landslide movement calculation model for the local area near the landslide center, with the center of the landslide as the center, and the process is as follows:

[0050] (1.1) Based on the original river channel terrain, the center of the landslide is taken as the model center, and the modeling range is ensured to be within the model boundary when the landslide stops moving.

[0051] (1.2) According to the engineering geological profile of the landslide, the potential sliding surface of each profile is determined.

[0052] (1.3) According to the potential sliding surface determined in each profile and the landslide limit on the ground surface, a three-dimensional sliding surface of the landslide is established.

[0053] (1.4) The landslide is determined as a closed space surrounded by the sliding surface and the ground surface, and the space where the landslide is located is discretized using spherical particles. In the discretization process, the particle size range of the spherical particles is first determined, and then the spherical particles of the given particle size range are filled in a large area covering the space where the landslide is located until the porosity of the space reaches the set porosity. Then the spherical particles outside the space where the landslide is located are deleted, and only the spherical particles inside the space are retained. Finally, the spherical particles inside the space where the landslide is located are balanced to form a close-contact spherical particle cluster, and the discretization of the landslide is completed.

[0054] (1.5) The surface of the landslide in the original ground surface is deleted, and the sliding surface of the landslide is connected with the original ground surface to form the bottom boundary of the landslide sliding, and the position is fixed. Then the bottom boundary of the landslide sliding is discretized using Wall units, and the side length of the Wall unit is greater than the particle size of the spherical particle.

[0055] (1.6) All spherical particles constituting the landslide and the discretized bottom boundary of the landslide movement are integrated to construct the landslide movement calculation model.

[0056] (2) The landslide movement is simulated by using a landslide movement calculation model, the influence of water on the landslide movement is considered, and the calculation is stopped until the landslide stops moving. In the simulation process, the information of all the spherical particles constituting the landslide is extracted, including the X coordinate, Y coordinate, Z coordinate and radius of the spherical center of each spherical particle, which is used for the terrain reconstruction of the water wave model in step 4).

[0057] In step (2), the process of simulating the landslide movement by using the landslide movement calculation model is as follows:

[0058] (2.1) According to the lithology of each rock layer in the landslide, a parallel bond model is used to represent the mechanical characteristics of the rock-soil mass, including strength characteristics and deformation characteristics. The calculation parameters in the parallel bond model are determined by using numerical simulation inversion based on the results of field tests, laboratory tests and stability analysis. The calculation parameters include parallel bond element parameters and linear elastic element parameters. A linear elastic model is used to represent the friction coefficient between the landslide and the sliding surface during the sliding process. The friction coefficient is the residual friction coefficient.

[0059] (2.2) The gravity, buoyancy and drag force are applied to the landslide in the landslide movement calculation model to simulate the landslide movement, and the dynamic evolution process of the landslide sliding, disintegrating and sliding into the river and accumulating in the river is obtained.

[0060] The buoyancy of the landslide during the water entry process is calculated by the volume of the water displaced. For a completely submerged spherical particle, the volume of the water displaced is equal to the volume of the spherical particle itself; when in a partially submerged state, the volume of the water displaced is calculated according to the volume of the spherical particle below the water surface.

[0061] Preferably, the drag force of the water acts on the submerged spherical particle as an external force, and the direction is opposite to the direction of the spherical particle movement. The calculation formula of the drag force is:

[0062] In the formula: is the comprehensive drag coefficient; is the density of the water; is the cross-sectional area of the spherical particle; is the velocity.

[0063] (3) According to the river terrain of the research area and the sliding surface of the landslide, a surge evolution calculation model is constructed by using a water wave model, and the node coordinates in the surge evolution calculation model are extracted as the initial terrain node coordinates. The river boundary in the surge evolution calculation model is set as an open boundary to avoid the reflection of the surge wave at the boundary of the model, and the water level in the surge evolution calculation model is set consistent with the research needs. By traversing each node of the surge evolution calculation model, the X coordinate, Y coordinate and Z coordinate of each node are extracted to provide the initial terrain for subsequent terrain updating.

[0064] The initial terrain of the surge evolution calculation model is the original terrain of the river channel in the study area, and the terrain at the landslide body is the sliding surface of the landslide body.

[0065] (4) The terrain of the surge evolution calculation model is reconstructed according to the X coordinate, Y coordinate, Z coordinate and radius of the ball center of each ball particle in the numerical simulation process of the landslide body motion in step (2), and then the terrain changing with the motion of the landslide body is established.

[0066] In step (4), the step of reconstructing the terrain of the surge evolution calculation model is:

[0067] (4.1) The X and Y coordinates of the initial terrain node of the water wave model in the vertical projection area of a single ball particle are searched, the height h of the upper surface of the ball particle relative to the X and Y coordinates is calculated, and the calculation formula is: .

[0068] In the formula: h is the height of the upper surface of the ball particle relative to the X and Y coordinates; X, Y and Z coordinates of the ball center; R is the radius of the ball particle; X and Y coordinates of the initial terrain node in the vertical projection range of the ball particle.

[0069] Then, the height h of the upper surface of the ball particle relative to the X and Y coordinates is compared with the Z coordinate height of the initial terrain node at the X and Y coordinates. If the height of the upper surface of the ball particle relative to the X and Y coordinates is higher than the Z coordinate height of the initial terrain node at the X and Y coordinates, the Z coordinate height of the initial terrain node at the X and Y coordinates is updated using the height of the upper surface of the ball particle relative to the X and Y coordinates. If it is smaller, the Z coordinate height of the terrain node is kept unchanged.

[0070] (4.2) Steps (4.1) are repeated to traverse all ball particles. During the traversal process, if the height of the initial terrain node has been updated, the updated terrain node height is used for comparison. For the terrain outside the landslide influence area, the initial terrain data is kept unchanged because it is not affected by the landslide motion.

[0071] (4.3) Steps (4.1) and (4.2) are performed at each terrain change time of the landslide motion calculation model to construct the terrain of the surge evolution calculation model affected by the motion of the landslide body at the current time. At the beginning of each update time, the initial terrain of the surge evolution calculation model is used as the basis. The reconstructed terrain of the surge evolution calculation model at each time is integrated to form the terrain of the surge evolution calculation model changing with the motion of the landslide.

[0072] (4.4) After the landslide stops moving, the terrain of the surge evolution calculation model no longer changes, and the reconstructed terrain at the time when the landslide stops is kept unchanged.

[0073] Preferably, in step (4.1), before reconstructing the terrain of the water wave model, the initial terrain node range required to be searched in the water wave model is determined based on the modeling area of the landslide movement calculation model, so as to avoid searching all the terrain nodes in the water wave model and causing a large amount of calculation redundancy.

[0074] Further, in step (4.1), during the node searching process for each ball particle, the K-D Tree method is used to improve the searching efficiency.

[0075] (5) Based on the surge evolution calculation model, the terrain changing with the landslide movement is introduced into the water wave model for surge evolution numerical simulation, and time iteration calculation is performed to obtain the surge generation and propagation process, and the maximum wave height at the thalweg in the surge evolution calculation model is extracted.

[0076] (6) The effectiveness of the calculation result is verified by using the landslide surge large-scale physical similarity model test.

[0077] The verification method is to perform a landslide surge large-scale physical model test under the same scenario, monitor the surge wave process by arranging measuring points in the landslide surge large-scale physical model, obtain the maximum wave height of each measuring point, and then compare the maximum wave height of each measuring point obtained by the landslide surge large-scale physical similarity model test with the maximum wave height of the corresponding position in the calculation result to verify the effectiveness of the calculation result.

[0078] Embodiment

[0079] Taking a landslide surge in a mountainous area as an example, the variable terrain landslide surge simulation method based on DEM and water wave model of the present application is illustrated.

[0080] (1) According to the terrain characteristics of the research area, a local area near the landslide body is selected, and a landslide movement calculation model is established by using the DEM method. The river channel terrain is established according to the actual terrain of the research area, and the sliding surface is obtained from the potential sliding surface in each landslide profile. The established landslide movement calculation model is shown in Figure 2 The landslide body is discretized by using ball particles with an average particle size of 3 m to form a landslide body composed of 60,131 ball particles. According to the mechanical properties of each rock layer and the sliding surface in the landslide body, the mechanical parameters of the rock-soil body and the sliding surface are assigned. Among them, the influence of water on the landslide movement is considered.

[0081] (2) The landslide movement calculation model is used to perform numerical simulation of the landslide movement, and the landslide movement evolution process is obtained, as shown in Figure 3The landslide body starts from the static state, slides along the sliding surface, and the trailing edge sliding speed is significantly greater than the leading edge (t = 15 s). Then the landslide body slides into the river channel, and the sliding speed gradually decreases (t = 25 s). At t = 100 s, the landslide body stops moving and accumulates in the river channel. Extract all ball particle information constituting the landslide body during the landslide movement, including the X coordinate, Y coordinate, Z coordinate and radius of the ball center of each ball particle, for reconstructing the terrain of the water wave model.

[0082] (3) According to the river terrain of the research area and the sliding surface of the landslide body, a surge evolution calculation model is constructed using the water wave model, as shown in Figure 4 The upstream boundary of the surge evolution calculation model is an open boundary to avoid the reflection of the surge wave at the boundary. The downstream is the dam. Extract the node coordinates in the surge evolution calculation model as the initial terrain node coordinates to provide the initial terrain for subsequent terrain update.

[0083] (4) According to the movement characteristics of the landslide body, the terrain of the surge evolution calculation model is reconstructed, and then the terrain changing with the movement of the landslide body is established. The terrain reconstruction of the surge evolution calculation model at a typical moment is shown in Figure 5 Extract all ball particle information, including the X coordinate, Y coordinate, Z coordinate and radius of the ball center of each ball particle (t = 100 s) Figure 5a Then update the elevation of each node in the surge evolution calculation model using the information of each ball particle, while the terrain outside the landslide influence area remains unchanged (t = 105 s) Figure 5b

[0084] (5) Import the terrain changing with the movement of the landslide body into the surge evolution calculation model, set the water level to be the same as the research water level, and perform surge evolution numerical simulation to obtain the spatio-temporal evolution process of the surge as shown in Figure 6 Under the influence of terrain change in the water wave model, the water body starts to move (t = 10 s). Under the continuous change of the terrain, the surge evolution calculation model gradually produces a surge and propagates to the opposite shore and upstream and downstream in a circular arc shape (t = 20 s). Then the surge propagates along the river channel (t = 60 s), and reaches the dam at about t = 190 s.

[0085] (6) Extract the maximum wave height at the thalweg of the surge evolution calculation model, and compare it with the physical model test results of the landslide surge large-scale physical similarity model test to verify the effectiveness of the calculation results, as shown in Figure 7 It can be seen that the numerical calculation results are highly consistent with the physical model test results, proving the effectiveness of the calculation results.​

Claims

1. A method for simulating a variable-terrain landslide surge based on a DEM and a water wave model, characterized in that: The method comprises the following steps: (1) A DEM method is used to establish a landslide movement calculation model with the center of the landslide body as the center, and the process is as follows: a three-dimensional sliding surface of the landslide body is established from the sliding surface of the profile of the landslide body and the landslide limit at the original ground surface; after the closed space formed by the sliding surface and the original ground surface in the landslide body is discretized by using spherical particles, the surface of the landslide body in the original ground surface is deleted, and the sliding surface of the landslide body is connected with the original ground surface to form the bottom boundary of the landslide sliding; after the bottom boundary is fixed, the bottom boundary is discretized by using a Wall unit; (2) The landslide movement numerical simulation is performed by using the landslide movement calculation model until the landslide body stops moving, and the X, Y and Z coordinates and the radius of the ball center of each spherical particle constituting the landslide body are extracted; (3) According to the river terrain and the sliding surface of the landslide body, a surge evolution calculation model is constructed by using a water wave model, and the node coordinates in the surge evolution calculation model are extracted as initial terrain node coordinates; the river boundary is set as an open boundary, and the X, Y and Z coordinates of each node are extracted by traversing each node of the surge evolution calculation model; (4) According to the X, Y and Z coordinates and the radius of the ball center of each spherical particle in the landslide movement numerical simulation in step (2), the terrain of the surge evolution calculation model is reconstructed, and then the terrain changing with the movement of the landslide body is established; (5) On the basis of the surge evolution calculation model, the terrain changing with the movement of the landslide body is introduced into the water wave model to perform surge evolution numerical simulation, and time iteration calculation is performed, and the maximum wave height at the thalweg of the surge evolution calculation model is extracted; (6) A large-scale physical similar model test of landslide surge is performed, and the maximum wave height of the measuring point is obtained; the maximum wave height of the measuring point is compared with the maximum wave height of the corresponding position in the surge evolution calculation model in step (5), and the accuracy of the calculation result in step (5) is verified. 2.The DEM and water wave model based variable terrain landslide surge simulation method according to claim 1, characterized in that: In step (1), the process of discretizing the closed space formed by the sliding surface and the ground surface in the landslide body by using spherical particles is as follows: firstly, the particle size interval of the spherical particles is determined, then the spherical particles with a given particle size interval are filled in a region covering the space where the landslide body is located, until the porosity of the space reaches a set porosity; the spherical particles outside the space where the landslide body is located are deleted, and finally the spherical particles inside the space where the landslide body is located are balanced initially to form a cluster of contacted spherical particles. 3.The DEM and water wave model based variable terrain landslide surge simulation method according to claim 1, characterized in that: In step (4), the steps of reconstructing the terrain of the surge evolution calculation model are as follows: (4.1) Search the X, Y coordinates of the initial terrain node of the water wave model in the vertical projection area of a single spherical particle, calculate the elevation h of the upper surface of the spherical particle relative to the X, Y coordinates, and the calculation formula is: ; In the formula: is the elevation of the upper surface of the spherical particle relative to the X, Y coordinates; is the X coordinate of the center of the sphere, is the Y coordinate of the center of the sphere, is the Z coordinate of the center of the sphere; and R is the radius of the spherical particle; is the X, Y coordinates of the initial terrain node of the water wave model in the vertical projection area of the spherical particle; If the elevation of the upper surface of the spherical particle relative to the X and Y coordinates is higher than the elevation of the initial terrain node Z coordinate at the X and Y coordinates, the elevation of the initial terrain node Z coordinate at the X and Y coordinates is updated by using the elevation of the upper surface of the spherical particle relative to the X and Y coordinates, otherwise the elevation of the terrain node Z coordinate remains unchanged; (4.2) Steps (4.1) are repeated until all spherical particles are traversed, and during the traversal process, if the elevation of the initial terrain node has been updated, the updated terrain node elevation is used for comparison; (4.3) Perform steps (4.1) and (4.2) at each topographic change time of the landslide motion calculation model, and construct the topography of the surge evolution calculation model corresponding to the current time landslide motion; at the beginning of each update time, the initial topography of the surge evolution calculation model is used as the basis, and the reconstructed topography of the surge evolution calculation model at each time is integrated to form the topography of the surge evolution calculation model changing with the landslide motion; (4.4) After the landslide stops moving, the topography of the surge evolution calculation model is unchanged.

4. The DEM and water wave model based variable-terrain landslide surge simulation method according to claim 1, characterized in that: In step (1), after fixing the bottom boundary, the bottom boundary is discretized by using Wall elements, and the side length of the Wall element is greater than the particle size of the spherical particle.

5. The DEM and water wave model based variable-terrain landslide surge simulation method according to claim 1, characterized in that: In step (1), according to the engineering geological profile of the landslide body, the sliding surface of each profile is determined.

6. The DEM and water wave model based variable-terrain landslide surge simulation method according to claim 1, characterized in that: In step (2), the process of numerical simulation of landslide motion by using the landslide motion calculation model is as follows: (2.1) The parallel bond model is used to represent the strength characteristics and deformation characteristics of the rock-soil mass; The linear elastic model is used to represent the friction coefficient of the landslide body with the sliding surface during the sliding process; (2.2) The gravity, buoyancy and drag force are applied to the landslide body in the landslide motion calculation model to simulate the landslide motion, and the process of the landslide body sliding, deforming and disintegrating, sliding into the river, and accumulating in the river is obtained.

7. The DEM and water wave model based variable-terrain landslide surge simulation method according to claim 6, characterized in that: In step (2.2), the drag force acts on the submerged spherical particle in the opposite direction of the motion of the spherical particle, and the formula for calculating the drag force is: ; wherein, is the integrated drag coefficient; is the density of the water body; is the cross-sectional area of the spherical particle; is the sliding velocity of the spherical particle.

8. The DEM and water wave model based variable-terrain landslide surge simulation method according to claim 6, characterized in that: In step (2.2), the buoyancy of the landslide body during the water entry process is calculated by the volume of the water displaced, and the volume of the water displaced by the completely submerged spherical particle is equal to the volume of the spherical particle itself; the volume of the water displaced by the partially submerged spherical particle is calculated according to the volume of the spherical particle below the water surface.

9. The DEM and water wave model based variable-terrain landslide surge simulation method according to claim 1, characterized in that: In step (3), the initial topography of the surge evolution calculation model is the original topography of the river, and the topography at the landslide body is the sliding surface of the landslide body.

10. The DEM and water wave model based variable-terrain landslide surge simulation method according to claim 3, characterized in that: In step (4.1), the K-D Tree method is used to perform node search on the spherical particles.

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