A method for generating a large-scale discrete element model of discontinuous graded soil

Abstract

The present invention provides a method for generating a large-scale discrete element model of discontinuous graded soil, which includes: (1) creating soil particle materials and setting soil intrinsic parameters and mesoscopic parameters of the contact model; (2) creating a 3D penetrometer geometric model for assisting in model layering generation and impact simulation; (3) importing the geometric model into the EDEM software; (4) creating a soil particle factory for layering generation of the model; (5) generating particles with different scale factors in the soil particle factory; (6) selecting different geometric model combinations for assisting in model layering generation in step (2) to generate a model for simulation; (7) importing the 3D penetrometer geometric model in step (2) into the model generated in the above step (6) for impact penetration dynamics simulation. The present invention can realize the construction of a large-scale discrete element model of discontinuous graded soil, and can effectively solve the problem that the number of particles in a large-scale model generated from fine-grained soil is too large to be effectively calculated.

Description

Technical Field

[0001] The present invention relates to the technical field of dynamic response analysis of soil, and particularly relates to a method for generating a large-scale discrete element model of discontinuous gradation soil. Background Art

[0002] The dynamic response analysis of soil is one of the most complex and challenging problems in computational geomechanics. The penetrometer is widely used as an in-situ measurement tool for evaluating the mechanical properties of soil. During the penetration process, the contact surface between the penetrometer and the soil is constantly changing. It is necessary to consider the relative incompressibility of the soil in a short time interval, the non-uniformity of stress-strain behavior, and the rate dependence of soil stiffness and strength, etc. The research on the dynamic response and mechanism therein is the basis for quantifying mechanical relationships and model construction and modification. And the use of simulation is an indispensable means for carrying out mechanism analysis. Simulation can also carry out working conditions that cannot be achieved in experiments and reduce experimental costs. The finite element simulation is based on the concept of continuous medium and can only describe the overall force-bearing behavior of the soil, and cannot accurately obtain the large deformation process and the change of microscopic information of the soil. The discrete element method can analyze the force and motion laws between soil particles from the mesoscopic scale, so as to realize the simulation of the complex mechanical behavior and its motion process of the particles, and has become a common method for studying particle dynamics and is widely used to simulate the interaction problems between soil and tools.

[0003] The commonly used software for discrete element simulation is PFC and EDEM. Among them, PFC is mainly implemented through commands and is relatively flexible, but it is difficult to simulate complex geometric bodies, and cannot use GPU parallel computing, and the efficiency of generating particle models is low. EDEM has a mature operation interface, can quickly realize the modeling of complex geometric structures by importing CAD geometric models, and has a secondary development interface (API interface) based on the C++ language, supporting the customization of complex dynamic models.

[0004] The discrete element model used for engineering analysis is close to the actual model size, can exclude the influence of size effect and boundary effect, and the simulation results are more accurate. However, when generating a large-scale model of discontinuous gradation fine-grained soil, there will be a problem that the number of particles is too large to perform high-efficiency calculations. Especially when it comes to the impact penetration simulation of the cone or pile-soil interaction, there will be a significant particle size effect problem due to extremely uneven particles at the conical tip. Most of the existing discrete element simulation models are scaled down to generate smaller-scale models through the operation of PFC commands, or simplified by scaling the particle size, or generating semi-section, 1 / 4 size or smaller models after scaling the particle size by a large multiple to reduce the total number of particles, as shown in Figure 11 (a), but this method is not applicable to materials considering particle gradation because the randomly generated particle size distribution will be uneven. As shown inFigure 11 (As shown in (b), even though the method of particle refinement is adopted, although the finally generated model is a large-scale model, the particle size is large and it is a single-size particle, without considering the particle gradation. The closest implementation scheme to the present invention is to achieve particle refinement through the PFC command, considering the particle gradation, but the particle gradation distribution is relatively uniform and there is no need to consider the problem of particle size effect, as Figure 11 (c) shows. In addition, due to the disadvantage of low PFC operation efficiency, this method is not suitable for generating large-scale models, and at the same time, it cannot realize the modeling of complex geometric bodies, and the selection of the layering method and the scale factor of particle size scaling during the refinement process need to be continuously adjusted and verified through the "trial and error" method to find suitable parameters, with low efficiency. At present, the method for generating a large-scale discrete element model of discontinuous graded soil based on EDEM technology is still blank.

[0005] The problem of generating a large-scale discrete element model for discontinuous graded soil, especially fine-grained soil with extremely uneven particle distribution, has not been solved. To generate a discrete element model of such soil or granular materials, the refinement method of the relevant model and the determination of the scaling ratio parameter are crucial. On the basis of generating an appropriate number of particles considering the computational efficiency, the boundary effect and the particle size effect need to be considered simultaneously. Summary of the Invention

[0006] In view of the technical problems existing in the above background technology, the present invention proposes a method for generating a large-scale discrete element model of discontinuous graded soil, with reasonable conception, which can realize the construction of a large-scale discrete element model of discontinuous graded soil and can effectively solve the problem that the number of particles in the large-scale model generated by fine-grained soil is too large to be effectively calculated.

[0007] To solve the above technical problems, a method for generating a large-scale discrete element model of discontinuous graded soil provided by the present invention mainly includes the following steps:

[0008] (1) Create soil particle materials and set soil intrinsic parameters and mesoscopic parameters of the contact model;

[0009] (2) Create a 3D penetrometer geometric model for assisting in model layering generation and impact simulation;

[0010] (3) Import the geometric model for assisting in model layering generation into EDEM software;

[0011] (4) Create a soil particle factory for layering to generate the model;

[0012] (5) Generate particles with different scale factors in the soil particle factory;

[0013] (6) Select different geometric model combinations for assisting in model layering generation in the above step (2) to generate a model for simulation;

[0014] (7) Import the 3D penetrometer geometric model in step (2) into the model generated in step (6) above for impact penetration dynamics simulation, using the same speed and simulation parameters, and output the resistance value of the cone tip for comparison to select and verify a suitable model.

[0015] The method for generating a large-scale discrete element model of discontinuous graded soil, wherein the specific process of step (1) is as follows: First, create a soil particle material model, edit the name of the soil particle material, and set the intrinsic parameters and contact model parameters of the soil particle material model for generating soil particles; then add the particle shapes required for simulation to the soil particle material model and set the particle parameters, and the particle parameters include the initial particle radius size and particle size distribution; for discontinuous graded particles, on the basis of particle size scaling, set the percentage of each particle size particle through user-defined according to the results of the particle gradation experiment to complete the setting corresponding to the particle size distribution of the real material.

[0016] The method for generating a large-scale discrete element model of discontinuous graded soil, wherein: the intrinsic parameters include Poisson's ratio, true density, and shear modulus, which can be determined according to the physical property experiment of the particle material; the contact model parameters include the coefficient of restitution, static friction coefficient, and rolling friction coefficient.

[0017] The method for generating a large-scale discrete element model of discontinuous graded soil, wherein: step (1) can also use the Import function of BulkMaterial-Material-particle to import an external excel table containing information on particle size distribution, so as to complete the setting corresponding to the particle size distribution of the real material.

[0018] The method for generating a large-scale discrete element model of discontinuous graded soil, wherein the specific process of step (2) is as follows: Establish a geometric model for assisting in the generation of model layers through a three-dimensional modeling software. Such a geometric model plays an isolation role for the discrete element models generated by using different scale factors for layering, and at the same time construct a 3D penetrometer geometric model for impact simulation.

[0019] The method for generating a large-scale discrete element model of discontinuous graded soil, wherein: when generating the geometric model in step (2), make the inner ring of the geometric model with the smallest diameter hollow, and use it to generate particles by setting a particle factory in the innermost ring area.

[0020] The method for generating a large-scale discrete element model of discontinuous gradation soil, wherein the specific process of step (3) is as follows: Import the geometric model generated in step (2) using the geometry import function of EDEM software, form different combinations of geometric models according to simulation requirements, and uniformly adjust the length unit to mm during import. Set the Poisson's ratio, density, shear modulus of the imported geometric model, and the contact parameters between the geometric model and soil particles with different scale factors.

[0021] The method for generating a large-scale discrete element model of discontinuous gradation soil, wherein the specific process of step (4) is as follows:

[0022] (4.1) For the innermost region of the combination of geometric models formed in step (3), first add a geometry for generating particles through EDEM software to form an innermost particle factory. The shape and size of the added geometry are consistent with the central region of the geometric model with the smallest diameter in step (2). Then, use the volume filling particle generation method for the geometry to generate soil particles in the innermost region.

[0023] (4.2) For the regions outside the innermost region of the different combinations of geometric models formed according to simulation requirements, directly use the volume filling particle generation method on each geometric model for assisting in model layer generation to generate soil particles in each region according to simulation requirements.

[0024] The method for generating a large-scale discrete element model of discontinuous gradation soil, wherein the specific process of step (5) is as follows: After setting the particle generation method in step (4), start from the central region with the smallest innermost diameter and sequentially set the proportion of soil types and the proportion of solid volume in the volume filling particle generation method; use the particle refinement method to make the particles generated in the innermost region the smallest, and the particle sizes generated in the outer regions increase sequentially.

[0025] The method for generating a large-scale discrete element model of discontinuous gradation soil, wherein the specific process of performing impact penetration dynamics simulation in step (7) is as follows:

[0026] Set the total calculation time of the impact penetration dynamics simulation to 0.1 s, and use 0.005 s as the storage time interval for data and calculation results; in the discrete element simulation, the Rayleigh time step T R is solved by the following formula:

[0027]

[0028] In the above formula, R is the radius of the particle, ρ is the density of the particle, G is the shear modulus, and v is the Poisson's ratio;

[0029] The Rayleigh time step T RDuring the solution process, the resistance value at the tip of the cone and the change in the number of contacts between the tip of the cone and the particles are solved simultaneously. The tip resistance is the force component along the Z-axis direction at the tip of the cone during the penetration process. The number of contacts between the particles at the tip of the cone is calculated using the coordination number. The coordination number refers to the number of contacts of each particle with another particle at any given time point, and the average coordination number is expressed as:

[0030]

[0031] where M i is the number of contacts of the i-th particle.

[0032] Adopting the above technical solution, the present invention has the following beneficial effects:

[0033] The method for generating a large-scale discrete element model of discontinuous gradation soil in the present invention is reasonably conceived, which can fill the gap in the method for generating a large-scale discrete element model applicable to discontinuous gradation soil based on EDEM technology. It is applicable to any fine-grained soil or granular material, and is also applicable to the generation of large-scale discrete element models of soil or granular materials with any particle gradation.

[0034] The scheme of the auxiliary geometric model combination in the present invention can realize the generation and effective comparison of various particle sizes. Compared with the method for generating a large-scale discrete element model in the PFC discrete element software, the model generation process and calculation efficiency of the present invention are higher.

[0035] The method for particle refinement processing in the present invention can realize the construction of a large-scale discrete element model of fine-grained soil or granular material, and can effectively solve the problem that the excessive number of particles in the large-scale discrete element model of fine-grained soil leads to low operation and calculation efficiency.

[0036] The different combination schemes of the geometric models generated by the auxiliary model layer by layer in the present invention can effectively solve the problem that the excessive number of particles in the generation of large-size models of granular materials with extremely uneven particle size distributions leads to inefficient calculation.

[0037] The different combination schemes of the geometric models generated by the auxiliary model layer by layer in the present invention can effectively solve the boundary effect problem and the particle size effect problem in the discrete element simulation calculation of the interaction between the cone and the granular material. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0039] Figure 1 This is a flowchart of the method for generating a large-scale discrete element model of discontinuous gradation soil according to the present invention;

[0040] Figure 2 This is a particle gradation curve graph related to the method for generating a large-scale discrete element model of discontinuous gradation soil according to the present invention;

[0041] Figure 3 This is a schematic diagram of generating a geometric model related to the method for generating a large-scale discrete element model of discontinuous gradation soil according to the present invention;

[0042] Figure 4 This is a schematic diagram of importing a geometric model related to the method for generating a large-scale discrete element model of discontinuous gradation soil according to the present invention;

[0043] Figure 5 This is a schematic diagram of adding a geometric body in the central region related to the method for generating a large-scale discrete element model of discontinuous gradation soil according to the present invention;

[0044] Figure 6 This is a schematic diagram of particle refinement related to the method for generating a large-scale discrete element model of discontinuous gradation soil according to the present invention;

[0045] Figure 7 This is a schematic diagram of the finally generated model and the total number of particles related to the method for generating a large-scale discrete element model of discontinuous gradation soil according to the present invention;

[0046] Figure 8 This is a comparison graph of calculation results related to the method for generating a large-scale discrete element model of discontinuous gradation soil according to the present invention;

[0047] Figure 9 This is a flowchart of simulating an impact penetration model related to the method for generating a large-scale discrete element model of discontinuous gradation soil according to the present invention;

[0048] Figure 10 This is a schematic diagram of the tip resistance being the force component along the Z-axis direction at the tip during the penetration process related to the method for generating a large-scale discrete element model of discontinuous gradation soil according to the present invention;

[0049] Figure 11 This is a schematic diagram of generating a discrete element model by PFC software. Specific embodiments

[0050] Next, the technical solutions of the present invention will be described clearly and completely in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0051] The following further explains and illustrates the present invention in conjunction with specific embodiments.

[0052] A method for generating a large-scale discrete element model of discontinuous gradation soil provided by this embodiment can solve the problem that there are too many particles in the generation of a large-size model of fine-grained soil with extremely uneven particle size distribution, resulting in inefficient calculation, and can avoid boundary effects and particle size effects of the cone and particles.

[0053] Taking the penetration of a cone into silty clay with discontinuous gradation as an example, first, through the liquid limit moisture content test, the curve of the cone penetration depth and the moisture content is obtained, so as to obtain the liquid-plastic limit of the soil and determine that the soil is silty clay. The particle size distribution curve is obtained by the sieving method. As Figure 2 shown, it can be seen from the results that its particles are very fine, with D 50 around 40um, while the D 50 of coarse-grained soils such as sandy soil is generally several hundred micrometers (D 50 refers to the particle size corresponding to when the cumulative particle size distribution percentage of a sample reaches 50%). By calculation, its curvature coefficient C C is 0.6, and the coefficient of uniformity C U is 21.1. The results show that the particle size distribution of this soil is discontinuous and the particles are extremely uneven. The large-scale model generation process for this type of fine-grained soil is shown in Figure 1 :

[0054] S100. Create soil particle materials and set soil intrinsic parameters and mesoscopic parameters of the contact model

[0055] First, create a soil particle material model. Edit the material names: soil1, soil2, soil3, soil4, soil5, and set the intrinsic parameters of the material model used to generate soil particles, such as Poisson's ratio, true density, shear modulus, etc. (The intrinsic parameters such as Poisson's ratio, true density, shear modulus, etc. can be determined based on the physical property experiments of the granular material), as well as parameters of the contact model (including coefficient of restitution, static friction coefficient, and rolling friction coefficient); then, right-click on the material model and add the particle shapes required for the simulation through "Add particle" (The software itself has different forms of particle models for selection, or after constructing a particle model through 3D software according to the simulation requirements, import the self-built particle model through "displayTemplates-Import" in the "Tools-options-particledisplay" option in the menu bar, and support importing STL type files), and set the particle parameters, including the initial particle radius size and particle size distribution; for discontinuous graded particles, based on the particle size scaling (Particle size scaling means magnifying based on the actual particle gradation distribution, and this process is completed synchronously during the model generation process, that is, when all particles in the model are generated simultaneously), according to the results of the particle gradation experiment (which is a conventional physical property experiment for measuring the size distribution or proportion of particles in geotechnics and needs to be completed before the simulation research work and serves as the basis for particle generation in the simulation work), set the percentage of each particle size through user-defined settings, and the external excel table containing information on particle gradation distribution can also be imported through the "Import" function in the "Size Distribution" module in "Bulk Material-Material-particle", so as to complete the setting corresponding to the actual material particle size distribution.

[0056] S200. Generate a 3D penetrometer geometric model for assisting in model layer generation and impact simulation

[0057] Use 3D modeling software such as CAD, solidworks, Rhino, etc. to establish a geometric model for assisting in model layer generation. Such a geometric model plays an isolation role for the discrete element model generated by different scale factors during layer generation, and at the same time, a 3D penetrometer geometric model for impact simulation can be constructed, as follows Figure 3 As shown, the purpose of the geometric model required for layer generation is to isolate the particles generated by different scale factors. The inner circle of the geometric model with the smallest diameter is made hollow and is used to generate particles by setting a particle factory in the innermost area (The shape and size of the geometric model can be adjusted according to specific requirements).

[0058] S300. Import the geometric model for assisting in model layer generation into the EDEM software

[0059] Import the geometric model designed in step S200 through the Import Geometry function in the Creator Tree module in EDEM, and form different combinations of geometric models according to the simulation requirements; as follows Figure 4 As shown, when importing, the length unit is uniformly adjusted to mm, and the Poisson's ratio, density, shear modulus of the imported geometric model, and the contact parameters between the geometric model and soil particles with different scale factors are set.

[0060] S400. Create a soil particle factory for hierarchical model generation

[0061] The way of generating particles in the particle factory can be selected according to specific requirements. One is to select the dynamic generation method, and parameters such as the total mass or total number of particles, generation speed, expected number or mass generated per second need to be given; the other is the static generation method such as Volume packing, and the filling ratio of particles, filling amount and particle generation time need to be given. Here, the Volume packing generation method is taken as an example, and particle generation is divided into two parts:

[0062] One is for the innermost circle (i.e., the central cylinder area with the smallest diameter) of the geometric model combination formed in step S300. First, add a geometry Factory for generating particles through the EDEM software (specifically, by right-clicking the AddGeometry function in the Geometries module of the EDEM software) to form the innermost circle of particle factories. The shape and size of the added geometry Factory are consistent with the central area of the geometric model with the smallest diameter in step (2). Then, use the volume filling particle generation method for the geometry Factory to generate soil particles in the innermost circle area (specifically, implemented through the Add volume packing function of the EDEM software), as Figure 5 shown;

[0063] The second is for the area outside the innermost circle of the different geometric model combinations formed according to the simulation requirements in step S300 above. According to the simulation requirements, directly on each geometric model used to assist in hierarchical model generation, also use the volume filling particle generation method to generate soil particles in each area (such as Figure 4 0.1 - 0 in) is implemented through the Addvolume packing function of the EDEM software).

[0064] S500. Generate particles with different scale factors in the soil particle factory

[0065] After setting the particle generation method in step S400, starting from the central area with the smallest diameter in the innermost circle, set the proportion of soil types and the proportion of solid volume in the particle generation method of volume filling in sequence (the soil types are soil1, soil2, soil3, soil4, soil5 from the inside to the outside, and the proportion is 100% for all), and select the particle type set in step S100, which are soil 1 (the innermost circle), soil2, soil3, soil4, soil5... In order to reduce the total number of particles and improve the calculation efficiency, the present invention adopts a particle refinement method, that is, the particles generated in the innermost circle are the smallest, and the particle sizes of the particles generated in the outer layer areas increase in sequence; the purpose is to reduce the total number of particles in the overall model without affecting the calculation results, so as to improve the calculation efficiency of the large-scale discrete element model; for the model with larger particles generated in the outer layer area that interacts very little with the contact body, according to the literature and the verification of this method, a scale factor of 1.5 is adopted, which can avoid the migration of small particles to the large particle layer, that is, the particle diameter of the basic particles in soil2 is 1.5 times that of soil1. Taking the particle gradation magnified by 20 times as an example, the particle diameter of the basic particles in the innermost circle is 2mm, as Figure 6 shown, and so on.

[0066] S600. Select different geometric model combinations used for assisting in the hierarchical generation of the model in step S200 to generate the model for simulation

[0067] Start solving to generate the discrete element model under different geometric model combinations. Set the time step for solving in the solution calculation module in EDEM. The time step for generating the model can be selected automatically, and the time can be 1s. If CPU calculation is selected, the grid size needs to be estimated. Click the Estimate Cell Size button in Simulator Setting to estimate, and finally click the start button in the visualization interface to generate.

[0068] Three discrete element models for verifying the experimental effect of the model generation method of the present invention are generated according to the above step S600, that is, select different cylinder geometric model combinations to generate different models. The model generated with 5C uses all the geometric models in Figure 3 to form 5 particle generation areas. The model generated with 4C uses the geometric models (b), (c), (d) in Figure 3 The model generated with 3C uses the geometric models (c), (d) in Figure 3 Finally, the generated models and the total number of particles are as shown in Figure 7 shown. The total number of particles is 808393, 2042028, and 4143195 respectively. If the hierarchical generation method is not adopted, the total number of particles is over 8 million.

[0069] S700. Import the 3D penetrometer model in step (2) into the model generated in step (6) above for impact penetration dynamics simulation, using the same velocity and simulation parameters, and output the resistance value of the cone tip for comparison to select and verify a suitable model. The calculation results are as Figure 8 shown. The calculation effect of the model obtained by the 4C treatment method is similar to that of 3C. The maximum resistance values are 599.5 N and 600.2 N respectively, and the error can be basically ignored. However, due to the smaller diameter of the intermediate action area in the 5C model, the inner ring model will have a large strain under the impact force, that is, the boundary effect affects the calculation results, and it can be seen that this model is not suitable. Through comparison, it is found that the total number of particles in the 4C model is appropriate, meeting the requirements of high-efficiency calculation, and at the same time, it can avoid the boundary effect. The 3C model has relatively too many particles. Through literature review, the rationality of the 4C model can be further corroborated, that is, when the width of the inner layer soil is greater than or equal to 23 times the radius of the penetrometer, the boundary effect can be reduced to an acceptable range. Currently, the inner ring width of the 3C model is 0.6 m, and the ratio to the penetrometer diameter is close to 34 times; the inner ring width of the 4C model is 0.4 m, and the ratio to the penetrometer diameter is close to 23 times. In addition, to obtain a stable cone tip resistance curve, the number of particles in contact with the cone tip should be no less than 13. As Figure 8 (c) shows, the total number of particles at the cone tip is 47 - 62.

[0070] The specific process of performing impact penetration dynamics simulation in step S700 above is as follows:

[0071] After completing steps S100 - S700 above, the model and basic parameters required for simulation are already available in the EDEM software; here, the total calculation time of the impact penetration dynamics simulation is set to 0.1 s, and 0.005 s is used as the storage time interval for data and calculation results;

[0072] In the discrete element simulation, the Rayleigh time step T R is a key number; this refers to the time it takes for a shear wave to propagate through solid particles; since the discrete element is an explicit calculation, the time step will directly determine the update of particle velocity and position. A too large time step will affect the results. The calculation formula is:

[0073]

[0074] In the above formula, R is the radius of the particle, ρ is the density of the particle, G is the shear modulus, and v is the Poisson ratio; this formula assumes that the relative velocity between contacting particles is very small; except for quasi-static systems, in practice, a part of this maximum value is used. For high coordination numbers (4 and above), a typical time step is 0.2T R (20%) has been proven to be appropriate; when the coordination number is low, 0.4T R(40%) is more appropriate; to make the calculation results more stable, the time step here is set to 0.1T R ;

[0075] During the calculation process, the resistance value at the tip of the cone and the change in the number of contacts between the tip of the cone and the particles are calculated simultaneously. The tip resistance of the cone is the force component along the Z-axis direction at the tip of the cone during the penetration process, as Figure 10 shown.

[0076] The number of contacts between the particles at the tip of the cone can be calculated using the coordination number. The coordination number refers to the number of contacts of each particle with another particle at any given time point, which is an important index for studying the contact characteristics of the particle system, related to the stability of the structural system, and reflects the microscopic stress structure characteristics inside the soil body and the dense and loose state of the model during the loading process; the average coordination number can be expressed as:

[0077]

[0078] where M i is the number of contacts of the i-th particle.

[0079] The present invention can effectively determine the appropriate model generation method and refinement method to solve the problem of generating a large-scale discrete element model for discontinuous graded soil, especially fine-grained soil with extremely uneven particle distribution.

[0080] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for generating a large-scale discrete element model of discontinuously graded soil, characterized in that: The following steps are involved: (1) Create soil particle materials and set soil intrinsic parameters and contact model microscopic parameters; (2) Create a 3D penetrometer geometric model for auxiliary model layer generation and impact simulation. When generating the geometric model, the inner circle of the geometric model with the smallest diameter is made hollow, and particles are generated in the innermost circle by setting up a particle factory; (3) Importing the geometric model used to assist in model layer generation into the EDEM software. The specific process is as follows: using the geometry import function of the EDEM software to import the geometric model generated in step (2), forming different geometric model combinations according to the simulation requirements, uniformly adjusting the length unit to mm during import, and setting the Poisson's ratio, density, shear modulus of the imported geometric model, as well as the contact parameters between the geometric model and soil particles of different scale factors; (4) Create a soil particle factory for the hierarchical generation model. The specific process is as follows: (4.1) For the innermost region of the geometric model combination formed in step (3), first, a geometric body for generating particles is added using EDEM software to form a particle factory in the innermost region. The shape and size of the added geometric body are consistent with the central region of the geometric model with the smallest diameter in step (2). Then, the volume filling particle generation method is used to generate soil particles in the innermost region of the geometric body. (4.2) For areas outside the innermost circle where different geometric model combinations are formed according to simulation requirements, soil particles in each area are generated directly using the volume filling particle generation method on each geometric model used to assist in model layer generation according to simulation requirements; (5) Generating particles of different scale factors in a soil particle factory; (6) Selecting different geometric models used to assist in model layer generation in step (2) above to combine and generate a model for simulation; (7) The 3D penetrometer geometric model in step (2) is imported into the model generated in step (6) to perform impact penetration dynamics simulation, using the same velocity and simulation parameters, and outputting the resistance value of the cone tip for comparison to select and verify the appropriate model; the specific process of impact penetration dynamics simulation is as follows: The total calculation time of the impact penetration dynamics simulation is set to 0.1s, and the storage time interval of data and calculation results is 0.005s; in the discrete element simulation, the Rayleigh time step is T R Solve by the following formula: ； In the above formula, R is the radius of the particle, ρ is the density of the particle, G is the shear modulus, v is Poisson's ratio; Rayleigh time step T R During the solution process, the changes in the resistance value at the cone tip and the number of contacts between the cone tip and the particles during the entire penetration process are simultaneously solved. The cone tip resistance is the force component along the axis Z direction at the cone tip during the penetration process; the number of contacts between the particles at the cone tip is calculated using the coordination number. The coordination number refers to the number of contacts between each particle and another particle at any given time point, and the average coordination number is expressed as: ； In the formula M i For the i The number of contacts of particles.

2. The method for generating a large-scale discrete element model of discontinuously graded soil according to claim 1, wherein: The specific process of step (1) is as follows: first, a new soil particle material model is created, the name of the soil particle material is edited, and the intrinsic parameters and contact model parameters of the soil particle material model used to generate soil particles are set; then, the particle shape required for simulation is added to the soil particle material model and the particle parameters are set, and the particle parameters include the initial particle radius size and particle size distribution; for discontinuously graded particles, based on the particle size scaling, the percentage of each particle size is set by the user according to the particle grading experimental results to complete the setting corresponding to the particle size distribution of the real material.

3. The method for generating a large-scale discrete element model of discontinuously graded soil according to claim 2, wherein: The intrinsic parameters include Poisson's ratio, true density and shear modulus, which can be determined based on the physical property experiments of the granular materials; The contact model parameters include the coefficient of restitution, the coefficient of static friction and the coefficient of rolling friction.

4. The method for generating a large-scale discrete element model of discontinuously graded soil according to claim 2, wherein: The step (1) can also use the Import function of Bulk Material-Material-particle to import external excel sheet of particle size distribution information, so as to complete the setting corresponding to the actual material particle size distribution.

5. The method for generating a large-scale discrete element model of discontinuously graded soil according to claim 1, wherein: The specific process of step (2) is as follows: a geometric model for assisting model layer generation is established through three-dimensional modeling software. Such a geometric model plays an isolating role for discrete element models generated layer by layer using different scale factors, and at the same time, a 3D penetrometer geometric model for impact simulation is constructed.

6. The method for generating a large-scale discrete element model of discontinuously graded soil according to claim 1, wherein: The specific process of step (5) is as follows: after setting the particle generation method in step (4), starting from the central area with the smallest inner circle diameter, the soil type ratio and solid volume ratio parameters in the volume filling particle generation method are sequentially set; using the particle refinement method, the particles generated in the innermost circle are the smallest, and the particle sizes of the particles generated in the outer layer area are successively larger.

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