System calibration and verification method for discontinuous graded cohesive soil DEM model

Abstract

The present invention provides a system calibration and verification method for a discontinuous gradation cohesive soil DEM model, which includes: (1) preliminary determination of the mesoscopic parameter values of the DEM model; (2) sensitivity analysis of each mesoscopic parameter of the DEM model; (3) combined with the sensitivity analysis results, step-by-step optimization and iterative analysis of each factor to obtain the optimized value range of the mesoscopic parameters of the DEM model; (4) further optimize the mesoscopic parameters of the DEM model based on the Box-Behnken experimental design to obtain multiple groups of optimized parameter combinations; (5) parameter verification. The present invention has a reasonable concept, integrating parameter calibration, accuracy verification and actual experiments, making the purpose of parameter calibration more clear, and can provide a more efficient and directional parameter calibration idea for cohesive soils with complex parameter calibration and few references, especially fine-grained soils or granular materials with extremely uneven particle gradation, and can realize the parameter calibration under quasi-static loading to the parameter calibration and verification under dynamic load simulation.

Description

Technical Field

[0001] The present invention relates to the technical field of mechanical manufacturing, and particularly relates to a system calibration and verification method for a discontinuous grading cohesive soil DEM model. Background Art

[0002] As an important tool for analyzing discontinuous medium mechanics, the discrete element method (DEM) has made remarkable progress in the fields of geomechanics and geotechnical engineering in recent years. Especially in the research of complex problems such as soil-structure interaction and large deformation failure mechanism, it shows unique advantages. Different from numerical methods based on the assumption of continuous medium (such as the finite element method FEM), DEM can reveal the dynamic response characteristics of granular materials at the mesoscopic scale by tracking the movement trajectories of particles and the evolution of force chains.

[0003] Constructing a high-precision soil DEM simulation model is the key to obtaining reliable results, and multiple factors need to be considered comprehensively, including issues such as particle size distribution, particle scaling size, and particle shape involved in the particle model generation process, as well as the determination of the contact model and the calibration of the mesoscopic parameters of the contact model. Among them, selecting a suitable contact model and accurately calibrating the model parameters are the primary tasks for accurately reflecting the macroscopic mechanical behavior of the soil, and parameter calibration is also the most difficult link in discrete element simulation.

[0004] Although there are already relatively rich calibration studies on sandy soil, cohesive soil, and soil with high water content at present, there are few reports on the calibration work for cohesive soil with discontinuous grading and extremely uneven particle distribution. On the one hand, viscous contact models (such as the JKR and EEPA models) are highly sensitive to parameters and need to balance the multiple coupling effects of adhesion force, elastoplastic deformation, and energy dissipation. On the other hand, cohesive soil belongs to fine-grained soil, with a very small average particle size and a large particle size span. When calibrating parameters, it is necessary to scale the particle size to generate the total number of particles that can meet the computing power. At the same time, the influence of particle size effect and boundary effect also needs to be considered. Since the particle characteristics directly affect the accuracy of model generation and simulation results, the above factors undoubtedly increase the difficulty of the calibration work for this type of soil.

[0005] Current DEM calibration methods mainly rely on time-consuming trial-and-error methods, that is, by continuously iterating parameter combinations to achieve the coincidence between simulation results and experimental results, or calibration experiments based on a single physical property (such as angle of repose, direct shear test, triaxial or cone penetration test), and using other software to optimize the design of calibration experiments. There are two major problems: one is the singularity of calibration objectives. Static mechanical parameters cannot accurately map the behavior of particle migration and contact failure under dynamic impact, resulting in limited extrapolation ability of the model. The parameters calibrated under quasi-static loading may not be suitable for characterizing the mechanical behavior of soil when disturbed, such as impact penetration or penetration force; the other is the non-uniqueness of parameter combinations, that is, there is no unique solution for volume characteristics, and different mesoscopic parameters may produce equivalent macroscopic responses. Therefore, further research is needed to develop a calibration process to obtain accurate and highly applicable parameters. Summary of the Invention

[0006] In view of the technical problems existing in the above background art, the present invention proposes a method for calibrating and verifying discrete element simulation parameter systems based on actual operation effects. Its concept is reasonable, integrating parameter calibration, accuracy verification and actual experiments, making the purpose of parameter calibration more clear. It can provide a more efficient and directional parameter calibration idea for cohesive soils with complex parameter calibration and few references, especially fine-grained soils or granular materials with extremely uneven particle size distributions, and can realize the calibration of mesoscopic parameters under quasi-static loading to the calibration and verification of parameters under dynamic load simulation.

[0007] To solve the above technical problems, a method for systematically calibrating and verifying a discontinuous gradation cohesive soil DEM model provided by the present invention includes the following steps:

[0008] (1) Preliminary determination of the values of mesoscopic parameters of the DEM model;

[0009] (2) Sensitivity analysis of each mesoscopic parameter of the DEM model;

[0010] (3) Combining the sensitivity analysis results, gradually optimizing and iteratively analyzing each factor to obtain the optimized value range of the mesoscopic parameters of the DEM model;

[0011] (4) Further optimizing the mesoscopic parameters of the DEM model based on the Box-Behnken experimental design to obtain multiple groups of optimized parameter combinations;

[0012] (5) Parameter verification.

[0013] The method for systematic calibration and verification of the discontinuous gradation cohesive soil DEM model, wherein the specific process of step (1) is as follows: Based on existing literature and angle of repose tests, and by using the built-in discrete element particle model database in EDEM software, determine the initial reference value range of the mesoscopic contact parameters of the DEM model as the reference basis for constructing the discrete element model.

[0014] The method for systematic calibration and verification of the discontinuous gradation cohesive soil DEM model, wherein: The mesoscopic contact parameters of the DEM model in step (1) include shear modulus, coefficient of restitution (COR), coefficient of static friction (CSF), coefficient of rolling friction (CRF), and JKR of free surface energy; the initial reference value range of the shear modulus is 2e +7 ~3e +7 , the initial reference value range of the coefficient of restitution COR is 0.60 - 0.90, the initial reference value range of the coefficient of rolling friction CRF is 0.3 - 0.6, the initial reference value range of the coefficient of static friction CSF is 1.00 - 1.40, and the initial reference value range of the JKR of free surface energy is 2.5 - 6.5.

[0015] The method for systematic calibration and verification of the discontinuous gradation cohesive soil DEM model, wherein the specific process of step (2) is as follows: Taking the shear strength σ and elastic modulus E as evaluation indexes, calculate by taking different values of the mesoscopic contact parameters of the DEM model, and compare and analyze the unit increments of σ and E; then, obtain the average value of the unit increments under different values as the basis for judging the sensitivity, and the calculation formulas are as (1) and (2):

[0016] ;

[0017] ;

[0018] In the above formulas (1)-(2), x and y are the values of the mesoscopic contact parameters of each DEM model;

[0019] Through comprehensive analysis of the above formulas (1)-(2), the sensitivity of the mesoscopic contact parameters of each DEM model can be obtained.

[0020] The method for systematic calibration and verification of the discontinuous gradation cohesive soil DEM model, wherein the specific process of the step-by-step optimization and iterative analysis of each factor in step (3) is as follows: According to the sensitivity analysis results of step (2), sequentially adjust the values of the mesoscopic contact parameters of the DEM model; taking the comparison result of the stress-strain curves of the direct shear simulation test and the direct shear laboratory test as the standard, further narrow the value range of the mesoscopic contact parameters of each DEM model and optimize the value interval of the mesoscopic contact parameters of each DEM model.

[0021] The systematic calibration and verification method of the discontinuous graded cohesive soil DEM model, wherein the optimized value range of the parameters obtained in step (3) is as follows: the elastic modulus is 3.5e+07 Pa, the coefficient of rolling friction CRF is 0.4 - 0.6, the coefficient of restitution COR is 0.70 - 0.85, the coefficient of static friction CSF is 1.0 - 1.5, and the free surface energy JKR is 3.0 - 6.5.

[0022] The systematic calibration and verification method of the discontinuous graded cohesive soil DEM model, wherein step (4) specifically includes the following steps:

[0023] (4.1) Orthogonal rotational experimental design and regression model

[0024] According to the optimized range of the discrete element model parameters obtained in step (3), a calibration test is designed based on the Box-Behnken method: that is, the coefficient of rolling friction CRF, the coefficient of restitution COR, the coefficient of static friction CSF, and the free surface energy JKR in the mesoscopic contact parameters of the DEM model are used as test factors, and the elastic modulus and shear strength are used as optimization objectives to design the test factor and level data;

[0025] Based on the Design-Expert software, an orthogonal rotational experiment is designed, and multiple regression fitting analysis is performed on the experimental factor combinations and the corresponding result data to obtain the polynomial regression model of the direct shear calibration test as:

[0026] ;

[0027] (4.2)Determination of parameter optimization and optimized parameter combinations

[0028] Based on the polynomial regression model in step (4.1) above, the mesoscopic contact parameters of the DEM model are optimized using the optimization function in the Design-expert software; the optimization criteria are set according to the result ranges of the elastic modulus and shear strength; the obtained optimization solutions are not unique, but rather multiple parameter combination schemes, and this result can be used as the basis for calibrating and verifying the model parameters under dynamic load conditions.

[0029] The systematic calibration and verification method of the discontinuous graded cohesive soil DEM model, wherein step (5) specifically includes the following steps:

[0030] (5.1)Based on the optimized parameter combinations obtained in step (4), taking the impact penetration simulation test as the verification means, first construct a discontinuous graded clay impact penetration DEM model based on the impact penetration test;

[0031] (5.2) Quantitatively analyze the time history curve of the resistance received by the cone tip of the impact penetration penetrometer in the impact penetration test, and compare it with the results of the indoor impact penetration test to obtain the test and simulation results under different working conditions. Taking the shear strength as the control index, when the relative error is less than 5%, calibrate the discontinuous graded silty clay, and calibrate the mesoscopic parameters under quasi-static loading and then calibrate and verify the parameters under dynamic loading simulation; when the relative error is not less than 5%, return to the step (4) to further optimize the mesoscopic parameters of the DEM model.

[0032] The system calibration and verification method of the discontinuous graded cohesive soil DEM model, wherein: in the impact penetration test, the setting of the contact relationship between soil particles and the impact penetration penetrometer geometry can initially be consistent with the parameters between particles. After determining the parameter combination closest to the test results, make small adjustments, and then make micro-adjustments in turn to make the calibrated parameters more accurate.

[0033] Adopting the above technical solution, the present invention has the following beneficial effects:

[0034] The system calibration and verification method of the discontinuous graded cohesive soil DEM model of the present invention is reasonably conceived. Based on the multi-step system calibration and verification method of the angle of repose experiment, direct shear or triaxial experiment, the purpose of parameter calibration is more clear and the verification is more comprehensive.

[0035] The present invention can improve the parameter calibration accuracy of discontinuous graded cohesive soil and fine-grained soil with extremely uneven particle distribution; the present invention can provide a more efficient and directional parameter calibration idea for cohesive soil with complex parameter calibration and few references, especially fine-grained soil or granular materials with extremely uneven particle gradation;

[0036] The present invention provides a new method for realizing the applicability from the calibration of mesoscopic parameters under quasi-static loading to the simulation of dynamic loading.

[0037] Different from the previous single-form calibration method based on a single physical property of soil (such as the natural angle of repose or shear characteristics), the present invention is a multi-step and continuously iteratively optimized system calibration method, which can overcome the problems of poor calibration accuracy and lack of a unique solution caused by the large discreteness of geotechnical tests in a single method. 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 the flowchart of the multi-step calibration and verification method involved in the systematic calibration and verification method of the discontinuous gradation cohesive soil DEM model of the present invention;

[0040] Figure 2 This is the particle size distribution curve of discontinuous gradation clay involved in the systematic calibration and verification method of the discontinuous gradation cohesive soil DEM model of the present invention;

[0041] Figure 3 This is based on existing literature and the angle of repose test diagram ((a) Angle of repose measuring instrument; (b) Virtual test of angle of repose; (c) Schematic diagram of angle measurement) involved in the systematic calibration and verification method of the discontinuous gradation cohesive soil DEM model of the present invention;

[0042] Figure 4 This is the direct shear test diagram ((a) Direct shear tester (b) Direct shear simulation test model) involved in the systematic calibration and verification method of the discontinuous gradation cohesive soil DEM model of the present invention;

[0043] Figure 5 This is the stress-strain curve diagram under different mesoscopic parameters involved in the systematic calibration and verification method of the discontinuous gradation cohesive soil DEM model of the present invention;

[0044] Figure 6 This is the single-factor sensitivity analysis diagram involved in the systematic calibration and verification method of the discontinuous gradation cohesive soil DEM model of the present invention;

[0045] Figure 7 This is the mesoscopic parameter step-by-step optimization analysis diagram involved in the systematic calibration and verification method of the discontinuous gradation cohesive soil DEM model of the present invention;

[0046] Figure 8 This is the impact penetration indoor test and simulation diagram involved in the systematic calibration and verification method of the discontinuous gradation cohesive soil DEM model of the present invention;

[0047] Figure 9 This is the comparison diagram of test and simulation results ((a) Under dry state (b) Under 20% water content) involved in the systematic calibration and verification method of the discontinuous gradation cohesive soil DEM model of the present invention. Detailed implementation manners

[0048] Next, the technical solutions of the present invention will be clearly and completely described 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.

[0049] The present invention will be further explained and illustrated below in conjunction with specific embodiments.

[0050] As Figure 1 shown, a system calibration and verification method for a discontinuous gradation cohesive soil DEM model provided in this embodiment takes the calibration of mesoscopic parameters of discontinuous gradation silty clay as an example. The soil sample is taken from Yangbajing, Tibet, with a depth of 0 - 60 cm; the basic physical properties and particle size distribution of the soil sample are shown in Table 1 and Figure 2 shown;

[0051] Table 1: Basic physical properties of silty clay

[0052]

[0053] The Hertz - Mindlin model with JKR is used as the contact model of the soil. The Hertz - Mindlin with JKR contact model not only considers the elastic deformation between particles but also the influence of the adhesion between particles on the particle motion law, and is applicable to simulating particle bonding and agglomeration phenomena caused by factors such as electrostatic force and moisture, and is widely used in the simulation of materials such as powders, crops, and soils. The mesoscopic parameters that need to be calibrated for the JKR contact model mainly include the rolling friction coefficient (CRF) between particles and between particles and geometric bodies, the static friction coefficient (CSF), the coefficient of restitution (COR), and the surface energy (JKR). The purpose of the calibration test is mainly to determine the mesoscopic parameters that can characterize the properties of the soil itself. Therefore, the present invention mainly takes the CRF, CSF, COR, and JKR parameters between particles as the main analysis objects.

[0054] The system calibration and verification method for the discontinuous gradation cohesive soil DEM model of the present invention specifically includes the following steps:

[0055] S100. Preliminary determination of the values of mesoscopic parameters of the DEM model

[0056] Based on existing literature and the angle of repose test (as Figure 3 shown), and by using the built - in discrete element particle model database in the EDEM software, determine the initial reference value ranges (shear modulus: 2e +7 ~3e +7 ; COR: 0.60 - 0.90; CRF: 0.3 - 0.6; CSF: 1.00 - 1.40; JKR: 2.5 - 6.5) of the mesoscopic contact parameters (including shear modulus, coefficient of restitution COR, static friction coefficient CSF, rolling friction coefficient CRF, and free surface energy JKR) of the DEM model, as the reference basis for constructing the discrete element model.

[0057] S200, Sensitivity Analysis of Each Mesoscopic Parameter

[0058] In the contact model, different mesoscopic parameters have different degrees of influence on macroscopic mechanical behavior. To avoid blindness in the calibration process and improve the calibration efficiency, it is first necessary to adjust each parameter and conduct a single-factor sensitivity analysis. According to the reference literature, the mesoscopic shear modulus has the greatest influence on macroscopic mechanical behavior. Therefore, based on the initial mesoscopic parameter value range determined in step S100, the mesoscopic shear modulus is initially set to 2.5e+7. Direct shear tests and triaxial tests are common methods for measuring the mechanical properties of soil. To calibrate the parameters of the DEM model, direct shear or triaxial virtual calibration experiments need to be carried out on the model samples. This invention takes the direct shear test as an example for illustration, as Figure 4 shown.

[0059] Taking the shear strength σ and elastic modulus E as evaluation indicators, by calculating different values of the mesoscopic contact parameters of the DEM model and comparing and analyzing the unit increments of σ and E, as Figure 5 shown; then, the average value of the unit increments under different values is obtained as the basis for judging the sensitivity magnitude, and the calculation formulas are as (1) and (2):

[0060] ;

[0061] ;

[0062] In the above formula, x and y are the values of each mesoscopic parameter; through the comprehensive analysis of the above formulas (1)-(2), the sensitivity magnitudes of the mesoscopic contact parameters of each DEM model can be obtained;

[0063] As Figure 6 shown, the single-factor analysis results show that the influence of CRF on the shear strength σ is the greatest, with a unit increment of 197.31, while the influence of COR on the elastic modulus E is the most significant, with a unit increment of 56.55, and the influence of JKR on both evaluation indicators is the smallest. Through comprehensive analysis, the single-factor sensitivity magnitude is CRF > COR > CSF > JKR.

[0064] S300, Step-by-step Optimization and Iterative Analysis of Each Factor to Obtain the Optimized Value Range of Parameters

[0065] Based on the sensitivity analysis results of the above step S200, the values of each mesoscopic parameter are adjusted in turn (shearmodulus > CRF > COR > CSF > JKR); taking the comparison result of the stress-strain curves between the direct shear simulation test and the direct shear laboratory test as the standard, multi-factor step-by-step optimization analysis is carried out to further narrow the value range of the mesoscopic contact parameters of each DEM model and optimize the value interval of the mesoscopic contact parameters of the DEM model; as Figure 7As shown; the optimized analysis results are as follows: the elastic modulus is 3.5e+07 Pa, the CRF is 0.4 - 0.6, the COR is 0.70 - 0.85, the CSF is 1.0 - 1.5, and the JKR is 3.0 - 6.5.

[0066] S400. Further optimize the parameters based on the Box-Behnken experimental design to obtain multiple groups of optimized parameter combinations;

[0067] S410. Orthogonal rotational experimental design and regression model

[0068] According to the optimized range of the discrete element model parameters obtained in step S300, design a calibration experiment based on the Box-Behnken method to reduce the workload of parameter calibration and avoid the blindness of parameter adjustment during the calibration process; take the rolling friction coefficient CRF, restitution coefficient COR, static friction coefficient CSF, and free surface energy JKR in the mesoscopic contact parameters of the DEM model as experimental factors, and the elastic modulus and shear strength as optimization objectives, and the experimental factor and level data are shown in Table 2.

[0069] Table 2. Simulation experimental factors and levels

[0070]

[0071] Designed an orthogonal rotational experiment based on Design-Expert software (the core is to balance the experimental efficiency and model accuracy; the specific steps are: select "Central Composite Design" (Central Composite Design) in Design-Expert; check the "Rotatable" or "Orthogonal" option according to requirements; input the factor range, generate the experimental matrix and execute the experiment; establish a quadratic regression model to optimize the parameters.) to conduct multi-factor simulation analysis. This experiment involves a total of 4 factors and 3 levels, and a total of 29 experimental points are designed for response surface analysis. The experimental points are divided into two categories: one category is the factorial points, with a total of 24; the other category is the central points in the zero point area, and the experiment is repeated 5 times to estimate the experimental error. The experimental factor combinations and corresponding results are shown in Table 3.

[0072] Table 3. Experimental factor combinations and corresponding results

[0073]

[0074] Perform multiple regression fitting analysis on the experimental data in Table 3, and the polynomial regression model of the direct shear calibration experiment obtained is:

[0075] ;

[0076] The determination coefficient R of the regression equation 2= 0.9922, adjusted determination coefficient adj - R 2 is 0.963, indicating that the model has an excellent fitting effect and can replace the real test data for analysis. The results of the analysis of variance (see Table 4) show that the F - value of the model > 1 and P = 0.0001 < 0.05, indicating that the model has significant differences and the model design is reasonable. The direct shear calibration test can be predicted according to this model.

[0077] Table 4. Y E Analysis of variance of the polynomial regression model

[0078]

[0079]

[0080] S420, Parameter optimization and determination of the optimized parameter combination

[0081] Based on the polynomial regression model in the above - mentioned step S410, the mesoscopic contact parameters of the DEM model are optimized by using the optimization function in the Design - expert software. The optimization criteria are set according to the result ranges of the elastic modulus and shear strength in Table 3. The obtained optimal solutions are not unique, but multiple parameter combination schemes, as shown in Table 5. This result can be used as the basis for calibrating and verifying the model parameters under dynamic load conditions.

[0082] Table 5. Different combinations of the optimal parameters

[0083]

[0084] S500, Calibration results and verification

[0085] To verify the accuracy and applicability of the system calibration method of the present invention, based on the optimal parameter combination determined in step S400, the impact penetration simulation test is used as the verification means. Based on the impact penetration test, first, a discontinuous - gradation clay impact penetration DEM model is constructed, as Figure 8 shown.

[0086] Quantitatively analyze the time - history curve of the resistance received by the tip of the impact penetration penetrometer in the impact penetration test (i.e., the time - history curve of the tip resistance), and compare it with the results of the impact penetration laboratory test. The test and simulation results under different working conditions (water content: 0%, 20%) are compared as Figure 9As shown, taking the shear strength as the control index and with a relative error less than 5%, the effectiveness of the calibration method of this system is verified, and it also shows that this method has good practicability in the dynamic load force simulation of soil-tool interaction. In the impact penetration test here, the setting of the contact relationship between particles and geometric bodies can initially be kept consistent with the parameters between particles and particles. After determining the parameter combination closest to the test results, small-scale adjustments are then made to gradually achieve fine-tuning to make the calibration parameters more accurate.

[0087] According to the parameter calibration process of the above steps S100~S400 and the parameter verification process of the above step S500, the mesoscopic contact parameters of discontinuous graded silty clay under impact load are determined, as shown in Table 6.

[0088] Table 6: Mesoscopic contact parameters of silty clay particles at different water contents

[0089]

[0090] The present invention can provide a more efficient and more directional parameter calibration idea for cohesive soils with complex parameter calibration and few reference documents, especially fine-grained soils or granular materials with extremely uneven particle gradation, and can realize the parameter calibration from mesoscopic parameters under quasi-static force to parameter calibration and verification under dynamic load force simulation.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; 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 systematic calibration and verification method for DEM model of discontinuous graded clay soil, characterized by , including the following steps: Step 1: Preliminary determination of the values ​​of the mesoscopic parameters of the DEM model; Step 2: Sensitivity analysis of each DEM model’s microscopic parameters; Step 3: Combined with the results of sensitivity analysis, each factor is gradually optimized and iteratively analyzed to obtain the optimal value range of the mesoscopic parameters of the DEM model; Step 4: Further optimize the mesoscopic parameters of the DEM model based on the Box-Behnken experimental design to obtain multiple sets of optimized parameter combinations; Step 5: Parameter verification; The specific process of step 2 is as follows: taking shear strength σ and elastic modulus E as evaluation indicators, calculating different values ​​of the microscopic contact parameters of the DEM model, and comparing and analyzing the unit increments of σ and E; then, obtaining the average value of the unit increment under different values ​​as the basis for judging the sensitivity, and the calculation formulas are as follows (1) and (2): ； ； In the above formulas (1)-(2), x and y are the values ​​of the microscopic contact parameters of each DEM model; Through comprehensive analysis of the above formulas (1)-(2), the sensitivity of the microscopic contact parameters of each DEM model can be obtained; The step 4 specifically comprises the following steps: Step 4.1: Orthogonal rotation experimental design and regression model According to the optimization range of discrete element model parameters obtained in step 3, a calibration test is designed based on the Box-Behnken method: that is, the rolling friction coefficient CRF, the restitution coefficient COR, the static friction coefficient CSF and the free surface energy JKR in the DEM model micro-contact parameters are used as test factors, the elastic modulus and the shear strength are used as optimization targets, and the test factors and level data are designed; Based on the orthogonal rotation test designed by Design-Expert software, a multivariate regression fitting analysis was performed on the test factor combination and the corresponding result data, and the polynomial regression model of the direct shear calibration test was obtained as follows: ； Step 4.2: Parameter optimization and determination of optimal parameter combinations Based on the polynomial regression model in step 4.1 above, the optimization function in the Design-expert software is used to optimize the micro-contact parameters of the DEM model; the optimization criteria are set according to the result range of the elastic modulus and shear strength; the obtained optimization solution is not unique, but a combination of multiple parameters. The result can be used as a basis for calibration and verification of model parameters under dynamic load conditions; The step 5 specifically comprises the following steps: Step 5.1: Based on the optimized parameter combination obtained in step 4, the impact penetration simulation test is used as a verification method. Based on the impact penetration test, a discontinuous graded clay impact penetration DEM model is first constructed; Step 5.2: Quantitatively analyze the time history curve of the resistance of the cone tip of the impact penetration probe in the impact penetration test, and compare it with the indoor test results of the impact penetration test to obtain the test and simulation results under different working conditions. Take the shear strength as the control index. When the relative error is less than 5%, the calibration of discontinuous graded silty clay is realized, and the calibration and verification of the parameters under dynamic load simulation are realized from the calibration of the mesoscopic parameters under quasi-static stress. When the relative error is not less than 5%, return to the step 4 to further optimize the mesoscopic parameters of the DEM model. In the impact penetration test, the setting of the contact relationship between soil particles and the impact penetration probe geometry can be initially kept consistent with the parameters between the particles. After the parameter combination closest to the test results is determined, small-range adjustments are made, and micro-adjustments are achieved in turn to make the calibration parameters more accurate.

2. The method for system calibration and verification of the discontinuous graded clay DEM model according to claim 1, characterized in that: The specific process of step 1 is: based on existing literature and repose angle tests, and through the discrete element particle model database built into the EDEM software, the initial reference value range of the DEM model micro-contact parameters is determined as a reference for constructing the discrete element model.

3. The method for system calibration and verification of the discontinuous graded clay soil DEM model as claimed in claim 2, characterized in that: The microscopic contact parameters of the DEM model in step 1 include shear modulus, restitution coefficient COR, static friction coefficient CSF, rolling friction coefficient CRF and free surface energy JKR; the initial reference value range of the shear modulus is 2e +7 ~3e +7 The initial reference value range of the coefficient of restitution COR is 0.60~0.90, the initial reference value range of the coefficient of rolling friction CRF is 0.3~0.6, the initial reference value range of the coefficient of static friction CSF is 1.00~1.40, and the initial reference value range of the free surface energy JKR is 2.5~6.

5.

4. The method for system calibration and verification of a discontinuously graded clay soil DEM model as claimed in claim 1, characterized in that: The specific process of the stepwise optimization and iterative analysis of each factor in step 3 is as follows: according to the sensitivity analysis results of step 2, the values ​​of the mesoscopic contact parameters of the DEM model are adjusted in sequence; based on the stress-strain curve comparison results of the direct shear simulation test and the direct shear indoor test, the value range of the mesoscopic contact parameters of each DEM model is further narrowed and the value range of the mesoscopic contact parameters of each DEM model is optimized.

5. The method for system calibration and verification of the discontinuous graded clay soil DEM model as claimed in claim 4, characterized in that: The parameter optimization ranges obtained in step 3 are: elastic modulus is 3.5e+07 Pa, rolling friction coefficient CRF is 0.4-0.6, restitution coefficient COR is 0.70-0.85, static friction coefficient CSF is 1.0-1.5, and free surface energy JKR is 3.0-6.5.

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