Construction Method of Discrete Element Model for Fracturing Performance of Pavement Structures Based on CZM

Abstract

This invention discloses a method for constructing a discrete element model (DEM) of pavement structure fracture performance based on the CZM (Concentrated Zymmetric Model), comprising the following steps: constructing a discrete particle model of the pavement structure using a DEM; classifying particle clusters in the discrete particle model and setting material properties; determining the contact type and contact model between the boundaries of different types of particle clusters; for the bilinear cohesive model, introducing two parameters—the bond strength of the pavement structure and the ratio of the slope of the descending segment to the slope of the ascending segment in the bilinear cohesive model curve—to construct a new bilinear cohesive model; rewriting the code and importing it into the DEM, inputting the two parameters to complete the construction of the CZM-based DEM of pavement structure fracture performance; using the DEM for simulation and conducting real experiments simultaneously, comparing the simulated data with the real experimental data to verify the accuracy of the DEM. This invention fills the gap in applying the DEM based on the cohesive model to three-point bending beam tests of pavement structures.

Description

Technical Field

[0001] This invention belongs to the field of pavement structure fracture performance prediction technology, specifically involving a method for constructing a discrete element model of pavement structure fracture performance based on CZM. Background Technology

[0002] As is well known, asphalt mixtures and cement-stabilized crushed stone mixtures are quasi-brittle materials. In actual performance testing of such quasi-brittle materials, the fracture performance is greatly affected by the geometry and size of the test specimen. Therefore, nonlinear fracture mechanics methods are often used to study the fracture behavior of such quasi-brittle materials.

[0003] For the fracture behavior of quasi-brittle materials, the cohesive zone model (CZM) can provide good prediction results and is currently widely used in the fracture behavior of asphalt mixtures, cement-stabilized crushed stone mixtures, polymers, and fiber composites under various loading conditions. However, in numerical simulation studies of pavement materials based on the CZM, most researchers use finite element method (FEM) software to perform numerical simulations of pavement materials and obtain the parameters of the CZM model through splitting tests, rarely using discrete element method (Particle Flow Code) software. Furthermore, the CZM model is a constitutive equation and cannot generate evolution graphs to show the evolution of cracks; therefore, discrete element method software is needed to graphically simulate the development of cracks.

[0004] Discrete element models (DEMs) can overcome many shortcomings in actual testing processes (i.e., macroscopic experiments), such as unstable test results and high test costs. Furthermore, DEMs have the advantage of allowing observation of the internal structure of pavement materials from a microscopic perspective, such as observing microscopic changes like crack propagation and structural damage. However, current DEM models mostly simulate materials in single pavement layers, such as asphalt mixtures in the surface layer or cement concrete in the base layer. Research on the overall pavement structure (i.e., treating the surface layer and base layer as a whole) is relatively limited. Therefore, it is necessary to develop a method for constructing a DEM model of pavement structural fracture performance based on CZM to address the problems existing in current technologies.

[0005] The invention patent with application publication number CN115481559A discloses a method for constructing a discrete element model of asphalt mixture based on intersection discrimination and convex optimization. Specifically, the method involves: setting a specified region in Matlab and placing aggregates within the specified region; importing the aggregate contour information into PFC2D to establish a polygonal wall corresponding to the aggregate contour; constructing the same specified region as in step 1 in PFC2D as the specified region wall; placing the polygonal wall from step 2 within the specified region wall, and then generating circular particles within the specified region wall to fill the entire specified region wall; simulating the aggregate composed of polygonal walls, identifying the small circular particles located outside all polygonal walls as asphalt mortar particles; and establishing a two-dimensional discrete element model of asphalt mixture with a porosity of vv. The invention patent with publication number CN117350141A discloses a method for simulating fatigue damage of recycled asphalt mixtures based on discrete element method (DEM). Specifically, the method involves: constructing a two-dimensional irregular convex polygon in a first designated region based on the target gradation; generating a DEM model filled with spheres in a second designated region; mapping the two-dimensional irregular convex polygon to the DEM model and integrating the DEM model based on the overlap between the two-dimensional irregular convex polygon and the spheres; grouping the asphalt mixture into new asphalt and old asphalt groups based on the relationship between the new aggregate group, the old aggregate group, and the asphalt group; constructing a contact based on the relationship between the new aggregate group, the old aggregate group, the new asphalt group, and the old asphalt group; and constructing a fatigue damage constitutive model of the recycled asphalt mixture based on the evolution law of the contact to simulate fatigue damage.

[0006] The aforementioned two patented technologies only construct discrete element models for materials in a single pavement layer (i.e., asphalt mixture and recycled asphalt mixture), rather than for the overall pavement structure (i.e., the surface layer and base layer as a whole). Therefore, the simulation results obtained from the discrete element models constructed based on these two patented technologies cannot represent the overall pavement structure. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a method for constructing a discrete element model of pavement structure fracture performance based on CZM. The construction method includes the following steps in sequence:

[0008] Step 1: Construct a discrete particle model of the road surface structure using the discrete element model;

[0009] Step 2: According to the type of aggregate, classify all aggregate particle clusters in the discrete particle model so that different types of aggregate particle clusters represent different types of aggregates. Set the internal and external properties of the material in the solid pavement structure corresponding to different types of aggregate particle clusters, and input the set internal and external properties of the material into the discrete element model.

[0010] Step 3: Determine the contact type and contact model between the boundaries of different types of aggregate particle clusters. The contact types include aggregate-aggregate contact, aggregate-cement contact, cement-cement contact, aggregate-asphalt contact, and asphalt-asphalt contact. The contact model corresponding to aggregate-aggregate contact is a linear model in the discrete element model, while the contact models corresponding to aggregate-cement contact, cement-cement contact, aggregate-asphalt contact, and asphalt-asphalt contact are all bilinear cohesive models.

[0011] Step 4: For the bilinear cohesive force model, introduce two parameters into it: the bond strength of the pavement structure and the ratio of the slope of the descending segment to the slope of the ascending segment in the bilinear cohesive force model curve, and then construct a new bilinear cohesive force model.

[0012] Step 5: Using Microsoft Visual Studio, rewrite the newly constructed bilinear cohesive model into code and import the code into the discrete element model. At the same time, input two parameters into the discrete element model: the bond strength of the pavement structure and the ratio of the slope of the descending segment to the slope of the ascending segment in the bilinear cohesive model curve, as well as other commonly used parameters, and then complete the construction of the discrete element model of pavement structure fracture performance based on CZM.

[0013] Step 6: In the discrete element model of pavement structure fracture performance based on CZM, set the boundary conditions, limiting conditions, loading conditions, and termination conditions of the test specimen. Then, conduct a simulation test on the fracture behavior of the test specimen and observe the evolution process of cracks in the test specimen in real time. When the simulation test reaches the termination condition, stop the simulation test, export the simulation test data, and plot the simulation curve of load changing with time.

[0014] Step 7: Fabricate a test specimen of the actual pavement structure in the laboratory, and set the same test specimen boundary conditions, test specimen limitation conditions, test loading conditions, and test termination conditions as the simulation test. Then, use a press to conduct a three-point bending beam test on the test specimen. When the test reaches the test termination condition, stop the test, export the test data, and plot the test curve of load change over time.

[0015] Step 8: Compare the simulated curves with the experimental curves to verify the accuracy of the discrete element model of pavement structure fracture performance based on CZM.

[0016] Preferably, in step one, the road structure is a cement-stabilized crushed stone base asphalt pavement structure, that is, the road structure includes a surface layer and a base layer, the paving material of the surface layer is asphalt mixture, and the paving material of the base layer is cement-stabilized crushed stone mixture.

[0017] In any of the above schemes, the preferred method for constructing the discrete particle model in step one includes the following steps in sequence:

[0018] Step (1): Construct a road structure model in the discrete element model and define the boundary of the road structure model;

[0019] Step (2): Generate aggregate boundaries in the pavement structure model according to the Monte Carlo method, and define all aggregate particles inside the aggregate boundaries as an aggregate particle cluster;

[0020] Step (3): Traverse all aggregate particles in all aggregate particle clusters, identify aggregate particles belonging to multiple aggregate particle clusters, delete the aggregate boundaries of the multiple aggregate particle clusters to which the aggregate particle belongs, and regenerate the aggregate boundaries.

[0021] Step (4): Repeat steps (2) to (3) until no more aggregate particles belonging to multiple aggregate particle clusters are identified. At this time, a particle aggregate with the same gradation as the actual test specimen is formed in the pavement structure model, and the stress between the particle aggregates in the pavement structure model is calculated to the equilibrium state, thus completing the construction of the discrete particle model.

[0022] This invention employs an aggregate generation method based on the aggregate boundary of a particle cluster. The aggregate morphology characteristics based on statistical theory in this method can be accurately reflected in the model. The particles are bonded to each other, and when the force at the contact point between the particles is greater than the bond strength, the bond breaks. The particles that have detached from the particle cluster can still be solved for forces independently.

[0023] In any of the above schemes, it is preferred that, in step two, the internal properties of the material include the material's density and damping, and the external properties of the material include the material's modulus, stiffness ratio, bond strength, and coefficient of friction.

[0024] Preferably, in any of the above schemes, in step four, the bond strength of the pavement structure is: In the formula, T C — Bond strength of pavement structure, MPa;

[0025] P max —The maximum load value in N in the bilinear cohesive model curve of the pavement structure;

[0026] L—Length of the road surface structure, in mm;

[0027] b—Width of the road surface structure, in mm;

[0028] h—Height of the pavement structure, mm;

[0029] The bilinear cohesive model curve is the load-crack opening displacement curve.

[0030] In any of the above schemes, preferably, in step four, the ratio of the slope of the descending segment to the slope of the ascending segment in the bilinear cohesive force model curve is [value missing]. In the formula,

[0031] K S-L —The ratio of the slope of the descending segment to the slope of the ascending segment in the bilinear cohesive model curve of the pavement structure;

[0032] K S —The slope of the descending segment in the bilinear cohesion model curve of the pavement structure;

[0033] K L —The slope of the rising segment in the bilinear cohesion model curve of the pavement structure;

[0034] T C — Bond strength of pavement structure, MPa;

[0035] δ f —Maximum crack opening displacement in the pavement structure, mm;

[0036] δ0—The displacement of crack opening in the pavement structure when the load reaches its peak value, in mm;

[0037] The bilinear cohesive model curve is the load-crack opening displacement curve.

[0038] In any of the above schemes, it is preferred that, in steps six and seven, the boundary conditions of the test specimen are the dimensions of the test specimen, which are 400 mm in length, 100 mm in width, and 100 mm in height.

[0039] In any of the above schemes, it is preferred that in steps six and seven, the test piece is limited to having a loading column at the center of the top of the test piece and support columns at the bottom of the test piece at a distance of 50mm from both ends.

[0040] In any of the above schemes, it is preferred that in steps six and seven, the test loading condition is constant speed loading, with a loading speed of 50 mm / min.

[0041] In any of the above schemes, preferably, in steps six and seven, the test ends when the load reaches 0.7 times the maximum load after the test specimen breaks. That is, the loading column applies a load to the test specimen at a constant rate. As the loading column moves downward, the load gradually increases, and cracks gradually appear in the test specimen. Just before the test specimen breaks, the load increases to its maximum. After the test specimen breaks, the load gradually decreases. When the load decreases to 0.7 times the maximum load, the simulation test and the test are stopped.

[0042] The present invention provides a method for constructing a discrete element model of pavement structure fracture performance based on CZM, which has the following beneficial effects:

[0043] (1) This invention fills the gap in the application of the discrete element method based on the cohesive force model (CZM) to the three-point bending beam test of pavement structure (treating the surface layer and base layer as a whole).

[0044] (2) The discrete element model constructed in this invention is for predicting the crack resistance performance of the overall pavement structure, rather than for predicting the crack resistance performance of a single pavement layer or a certain pavement material.

[0045] (3) This invention is applicable to the prediction of the crack resistance of cement-stabilized crushed stone base asphalt pavement structure, and can show the evolution process of cracks in cement-stabilized crushed stone base asphalt pavement structure, thereby realizing the prediction of crack propagation law. Attached Figure Description

[0046] Figure 1 This is a flowchart of a preferred embodiment of the method for constructing a discrete element model of pavement structure fracture performance based on CZM according to the present invention;

[0047] Figure 2 for Figure 1 The diagram shows the distribution of aggregate boundaries generated in the road structure model and the aggregate particle clusters formed inside the aggregate boundaries in the illustrated embodiment.

[0048] Figure 3 for Figure 1 The illustrated embodiment is a schematic diagram of the bilinear cohesive model constructed by introducing two parameters into the bilinear cohesive model: the bond strength of the pavement structure and the ratio of the slope of the descending segment to the slope of the ascending segment in the bilinear cohesive model curve.

[0049] Figure 4 for Figure 1 The schematic diagram of the crack evolution process of a common pavement structure in the embodiment shown is as follows: (a) is the crack initiation stage, (b) is the crack development stage, (c) is the crack penetration stage, and (d) is the macroscopic crack.

[0050] Figure 5 for Figure 1 The schematic diagram of the crack evolution process of the crack-resistant pavement structure in the embodiment shown is as follows: (a) is the crack initiation stage, (b) is the crack development stage, (c) is the crack penetration stage, and (d) is the macroscopic crack.

[0051] Figure 6 for Figure 1 The schematic diagram shown in the embodiment illustrates how the internal fracture energy of a common pavement structure changes with crack evolution, where: (a) represents the crack initiation stage, (b) represents the crack development stage, and (c) represents the crack penetration stage.

[0052] Figure 7 for Figure 1 The schematic diagram shown in the embodiment illustrates how the internal fracture energy of the crack-resistant pavement structure changes with crack evolution, where: (a) is the crack initiation stage, (b) is the crack development stage, and (c) is the crack penetration stage.

[0053] Figure 8 for Figure 1 The illustrated embodiment shows a photograph of the process of performing a three-point bending beam test on the test piece using a press in the laboratory.

[0054] Figure 9 for Figure 1 The embodiment shown uses a CZM-based discrete element model of pavement structure fracture performance to perform a three-point bending beam simulation test on the test specimen, and the simulated curve of load change over time is obtained.

[0055] Figure 10 for Figure 1 The embodiment shown is a test curve of load versus time obtained by performing a three-point bending beam test on the test piece using a press in the laboratory. Detailed Implementation

[0056] To further understand the invention, the following detailed description of the invention will be provided in conjunction with specific embodiments.

[0057] like Figure 1 As shown, according to a preferred embodiment of the method for constructing a discrete element model of pavement structure fracture performance based on CZM according to the present invention, the construction method includes the following steps in sequence:

[0058] Step 1: Construct a discrete particle model of the road surface structure using the discrete element model;

[0059] Step 2: According to the type of aggregate, classify all aggregate particle clusters in the discrete particle model so that different types of aggregate particle clusters represent different types of aggregates. Set the internal and external properties of the material in the solid pavement structure corresponding to different types of aggregate particle clusters, and input the set internal and external properties of the material into the discrete element model.

[0060] Step 3: Determine the contact type and contact model between the boundaries of different types of aggregate particle clusters. The contact types include aggregate-aggregate contact, aggregate-cement contact, cement-cement contact, aggregate-asphalt contact, and asphalt-asphalt contact. The contact model corresponding to aggregate-aggregate contact is a linear model in the discrete element model, while the contact models corresponding to aggregate-cement contact, cement-cement contact, aggregate-asphalt contact, and asphalt-asphalt contact are all bilinear cohesive models.

[0061] Step 4: For the bilinear cohesive force model, introduce two parameters into it: the bond strength of the pavement structure and the ratio of the slope of the descending segment to the slope of the ascending segment in the bilinear cohesive force model curve, and then construct a new bilinear cohesive force model.

[0062] Step 5: Using Microsoft Visual Studio, rewrite the newly constructed bilinear cohesive model into code and import the code into the discrete element model. At the same time, input two parameters into the discrete element model: the bond strength of the pavement structure and the ratio of the slope of the descending segment to the slope of the ascending segment in the bilinear cohesive model curve, as well as other commonly used parameters, and then complete the construction of the discrete element model of pavement structure fracture performance based on CZM.

[0063] Step 6: In the discrete element model of pavement structure fracture performance based on CZM, set the boundary conditions, limiting conditions, loading conditions, and termination conditions of the test specimen. Then, conduct a simulation test on the fracture behavior of the test specimen and observe the evolution process of cracks in the test specimen in real time. When the simulation test reaches the termination condition, stop the simulation test, export the simulation test data, and plot the simulation curve of load changing with time.

[0064] Step 7: Fabricate a test specimen of the actual pavement structure in the laboratory, and set the same test specimen boundary conditions, test specimen limitation conditions, test loading conditions, and test termination conditions as the simulation test. Then, use a press to conduct a three-point bending beam test on the test specimen. When the test reaches the test termination condition, stop the test, export the test data, and plot the test curve of load change over time.

[0065] Step 8: Compare the simulated curves with the experimental curves to verify the accuracy of the discrete element model of pavement structure fracture performance based on CZM.

[0066] In step one, the road structure is a cement-stabilized crushed stone base asphalt pavement structure, that is, the road structure includes a surface layer and a base layer. The paving material of the surface layer is asphalt mixture, and the paving material of the base layer is cement-stabilized crushed stone mixture.

[0067] In step one, the method for constructing the discrete particle model includes the following steps in sequence:

[0068] Step (1): Construct a road structure model in the discrete element model and define the boundary of the road structure model;

[0069] Step (2): Generate aggregate boundaries in the pavement structure model according to the Monte Carlo method, and define all aggregate particles inside the aggregate boundaries as an aggregate particle cluster;

[0070] Step (3): Traverse all aggregate particles in all aggregate particle clusters, identify aggregate particles belonging to multiple aggregate particle clusters, delete the aggregate boundaries of the multiple aggregate particle clusters to which the aggregate particle belongs, and regenerate the aggregate boundaries.

[0071] Step (4): Repeat steps (2) to (3) until no more aggregate particles belonging to multiple aggregate particle clusters are identified. At this time, a particle aggregate with the same gradation as the actual test specimen is formed in the pavement structure model, and the stress between the particle aggregates in the pavement structure model is calculated to the equilibrium state, thus completing the construction of the discrete particle model.

[0072] This embodiment employs an aggregate generation method based on aggregate boundaries within particle clusters. The statistically based aggregate morphology characteristics of this method are accurately reflected in the model. Particles are bonded together; when the force at the contact points exceeds the bond strength, the bond breaks, and the detached particles can still be solved for forces independently. The aggregate boundaries generated in the pavement structure model and the distribution of aggregate particle clusters formed within these boundaries are shown in the following example. Figure 2 As shown.

[0073] In step two, the internal properties of the material include its density and damping, and the external properties of the material include its modulus, stiffness ratio, bond strength, and coefficient of friction.

[0074] In step four, the bond strength of the road surface structure is In the formula,

[0075] T C — Bond strength of pavement structure, MPa;

[0076] P max —The maximum load value in N in the bilinear cohesive model curve of the pavement structure;

[0077] L—Length of the road surface structure, in mm;

[0078] b—Width of the road surface structure, in mm;

[0079] h—Height of the pavement structure, mm;

[0080] The bilinear cohesive model curve is the load-crack opening displacement curve.

[0081] In step four, the ratio of the slope of the descending segment to the slope of the ascending segment in the bilinear cohesion model curve is... In the formula,

[0082] K S-L —The ratio of the slope of the descending segment to the slope of the ascending segment in the bilinear cohesive model curve of the pavement structure;

[0083] K S —The slope of the descending segment in the bilinear cohesion model curve of the pavement structure;

[0084] K L —The slope of the rising segment in the bilinear cohesion model curve of the pavement structure;

[0085] T C — Bond strength of pavement structure, MPa;

[0086] δ f —Maximum crack opening displacement in the pavement structure, mm;

[0087] δ0—The displacement of crack opening in the pavement structure when the load reaches its peak value, in mm;

[0088] The bilinear cohesive model curve is the load-crack opening displacement curve.

[0089] This embodiment introduces two parameters into the bilinear cohesive model: the bond strength of the pavement structure and the ratio of the slope of the descending segment to the slope of the ascending segment in the bilinear cohesive model curve. The constructed bilinear cohesive model is as follows: Figure 3 As shown.

[0090] In steps six and seven, the boundary conditions of the test specimen are its dimensions: length 400mm, width 100mm, and height 100mm. The test specimen is constrained by a loading column at the center of its top and support columns 50mm from each end of its bottom. The loading condition is constant-rate loading at 50mm / min. The test ends when the load reaches 0.7 times the maximum load after the specimen breaks. Specifically, the loading column applies a constant load to the specimen; as the loading column moves downwards, the load gradually increases, and cracks gradually appear in the specimen. The load reaches its maximum just before the specimen breaks. After the specimen breaks, the load gradually decreases, and the simulation and testing stop when the load decreases to 0.7 times the maximum load.

[0091] This embodiment uses a discrete element model of pavement structure fracture performance based on CZM for simulation, wherein: the crack evolution process of ordinary pavement structure is as follows: Figure 4 As shown, (a) represents the crack initiation stage, (b) the crack development stage, (c) the crack penetration stage, and (d) the macroscopic crack; the crack evolution process of crack-resistant pavement structures is as follows. Figure 5 As shown, (a) represents the crack initiation stage, (b) the crack development stage, (c) the crack penetration stage, and (d) the macroscopic crack; the internal fracture energy of a typical pavement structure changes as the crack evolves, as follows: Figure 6As shown, (a) represents the crack initiation stage, (b) represents the crack development stage, and (c) represents the crack penetration stage; the internal fracture energy of the crack-resistant pavement structure changes as the crack evolves, as follows: Figure 7 As shown, (a) represents the crack initiation stage, (b) represents the crack development stage, and (c) represents the crack penetration stage.

[0092] In this implementation, the process of conducting a three-point bending beam test on the test piece using a press in the laboratory is shown in the following photographs. Figure 8 As shown; the simulated load-time curve obtained from the three-point bending beam simulation test of the test specimen using a discrete element model of pavement structure fracture performance based on CZM is shown in the figure. Figure 9 As shown; the load-time curve obtained from a three-point bending beam test on a test specimen using a press in the laboratory is shown in the figure. Figure 10 As shown in Table 1, the comparison results between the simulated test strength and the actual test strength of six pavement structures are presented.

[0093] Table 1 Comparison of simulated test strength and actual test strength for six pavement structures

[0094]

[0095]

[0096] from Figure 4-7 The evolution of cracks in the pavement structure and the change in internal fracture energy as the cracks evolve can be clearly observed. From Figure 9-10 As can be seen from Table 1, the simulated test intensity of the six pavement structures is close to the actual test intensity, with the deviation controlled within 10%. This indicates that the discrete element model of pavement structure fracture performance based on CZM constructed using the construction method of this embodiment has high accuracy.

[0097] The method for constructing a discrete element model of pavement structure fracture performance based on CZM in this embodiment has the following beneficial effects:

[0098] (1) It fills the gap in the application of the discrete element method based on the cohesive model (CZM) to the three-point bending beam test of pavement structure (treating the surface layer and base layer as a whole). (2) The constructed discrete element model is for predicting the crack resistance performance of the overall pavement structure, rather than for predicting the crack resistance performance of a single pavement layer or a certain pavement material. (3) It is suitable for predicting the crack resistance performance of cement-stabilized crushed stone base asphalt pavement structure, and can show the evolution process of cracks in cement-stabilized crushed stone base asphalt pavement structure, thereby realizing the prediction of crack propagation law.

[0099] Special Note: The technical solution of this invention involves numerous parameters, and the synergistic effects between these parameters must be comprehensively considered to achieve the beneficial effects and significant progress of this invention. Furthermore, the value ranges of each parameter in the technical solution were obtained through extensive experimentation. For each parameter and the combinations thereof, the inventors have recorded a large amount of experimental data; however, due to space limitations, the specific experimental data is not disclosed here.

[0100] Those skilled in the art will readily understand that the method for constructing the discrete element model of pavement structure fracture performance based on CZM of the present invention includes any combination of the inventive content and specific embodiments described in the above specification and the various parts shown in the accompanying drawings. Due to space limitations and for the sake of brevity, not all of these combinations have been described in detail. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for constructing a discrete element model of fracture performance of a pavement structure based on a CZM, characterized in that: The construction method comprises the following steps in sequence, Step one: build a discrete particle model of the pavement structure by a discrete element model; Step two: classify all aggregate particle clusters in the discrete particle model according to the types of aggregate, so that different types of aggregate particle clusters represent different types of aggregate, set the internal and external properties of the materials in the entity pavement structure corresponding to different types of aggregate particle clusters, and input the set internal and external properties of the materials into the discrete element model; Step three: determine the contact type and contact model between the boundaries of different types of aggregate particle clusters, that is, the contact type includes aggregate-aggregate contact, aggregate-cement contact, cement-cement contact, aggregate-asphalt contact, and asphalt-asphalt contact, wherein the contact model corresponding to aggregate-aggregate contact is a linear model in the discrete element model, and the contact models corresponding to aggregate-cement contact, cement-cement contact, aggregate-asphalt contact, and asphalt-asphalt contact are all bilinear cohesive force models; Step four: for the bilinear cohesive force model, introduce the bonding strength of the pavement structure and the ratio of the slope of the descending segment to the slope of the rising segment in the bilinear cohesive force model curve into the bilinear cohesive force model, and then construct a new bilinear cohesive force model; Step five: re-write the newly constructed bilinear cohesive force model into code by means of Microsoft Visual Studio software, import the written code into the discrete element model, input the bonding strength of the pavement structure, the ratio of the slope of the descending segment to the slope of the rising segment in the bilinear cohesive force model curve, and other commonly used parameters into the discrete element model, and then complete the construction of the pavement structure fracture performance discrete element model based on CZM; Step six: in the pavement structure fracture performance discrete element model based on CZM, set the test piece boundary conditions, test piece limiting conditions, test loading conditions, and test end conditions, then simulate the fracture behavior of the test piece, and observe the evolution process of the cracks in the test piece in real time; when the simulation test reaches the test end condition, stop the simulation test, export the simulation test data, and draw the simulation curve of load change over time; Step seven: make the test piece of the entity pavement structure in the laboratory, set the same test piece boundary conditions, test piece limiting conditions, test loading conditions, and test end conditions as the simulation test, then use a press to perform a three-point bending beam test on the test piece; when the test reaches the test end condition, stop the test, export the test data, and draw the test curve of load change over time; Step eight: compare the simulation curve with the test curve to verify the accuracy of the pavement structure fracture performance discrete element model based on CZM.

2. The method according to claim 1, wherein the method is characterized by: In step one, the pavement structure is a cement stabilized macadam base asphalt pavement structure, that is, the pavement structure comprises a surface layer and a base layer, the paving material of the surface layer is asphalt mixture, and the paving material of the base layer is cement stabilized macadam mixture.

3. The method according to claim 2, wherein: In step one, the construction method of the discrete particle model comprises the following steps in sequence, Step (1): constructing a pavement structure model in the discrete element model and defining the boundary of the pavement structure model; Step (2): generating aggregate boundaries in the pavement structure model according to the Monte Carlo method, and defining all aggregate particles inside the aggregate boundaries as an aggregate particle cluster; Step (3): traversing all aggregate particles in all aggregate particle clusters, identifying aggregate particles belonging to multiple aggregate particle clusters, and deleting the aggregate boundaries of the multiple aggregate particle clusters to which the aggregate particles belong, and regenerating the aggregate boundaries; Step (4): repeating steps (2) to (3) until no aggregate particles belonging to multiple aggregate particle clusters are identified, at which time a particle assembly with the same gradation as the actual test piece is formed in the pavement structure model, and the stress between the particle assemblies in the pavement structure model is calculated to an equilibrium state, i.e., the construction of the discrete particle model is completed.

4. The method according to claim 3, wherein the method is characterized by: In step two, the internal properties of the material include the density and damping of the material, and the external properties of the material include the modulus, stiffness ratio, cohesive strength, and friction coefficient of the material.

5. The method according to claim 4, wherein: In step four, the cohesive strength of the pavement structure is wherein, T C — Cohesive strength of the pavement structure, MPa; P max - maximum load value in the bilinear cohesive force model curve of the pavement structure, N; L - length of the pavement structure, mm; b - width of the pavement structure, mm; h - height of the pavement structure, mm; The bilinear cohesive force model curve is a load-crack opening displacement curve.

6. The method according to claim 5, wherein: In step four, the ratio of the slope of the descending segment to the slope of the ascending segment of the bi-linear cohesive force model curve is wherein, K S-L - the ratio of the slope of the descending section to the slope of the ascending section in the bilinear cohesion model curve of the pavement structure; K S - the slope of the descending section in the bilinear cohesive force model curve of the pavement structure; K L - the slope of the rising section in the bilinear cohesive force model curve of the pavement structure; T C — Cohesive strength of the pavement structure, MPa; delta f - maximum crack opening displacement of the pavement structure, mm; δ0 - crack opening displacement of the pavement structure when the load reaches the peak value, mm; The bilinear cohesive force model curve is a load-crack opening displacement curve.

7. The method according to claim 6, wherein the method is characterized by: In steps six and seven, the test piece boundary condition is the size of the test piece, which has a length of 400 mm, a width of 100 mm, and a height of 100 mm.

8. The method according to claim 7, wherein the method is characterized by: In steps six and seven, the test piece limiting condition is to set a loading column at the center of the top of the test piece and support columns at a distance of 50 mm from both ends of the bottom of the test piece.

9. The method according to claim 8, wherein the method is characterized by: In steps six and seven, the test loading condition is constant speed loading, with a loading speed of 50 mm / min.

10. The method according to claim 9, wherein the method is characterized by: In steps six and seven, the test end condition is that after the test piece breaks, the test is ended when the load reaches 0.7 times the maximum load, i.e., the loading column applies a load to the test piece at a constant rate, as the loading column moves downward, the load gradually increases, and the test piece gradually develops cracks. At the moment before the test piece breaks, the load increases to a maximum, and after the test piece breaks, the load gradually decreases. When the load decreases to 0.7 times the maximum load, the simulation test and the test are stopped.

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