Asphalt overlay layer state estimation method based on cement pavement fracturing state

Abstract

The invention relates to the technical field of road safety detection, in particular to an asphalt overlay state estimation method based on a cement pavement fracturing state, which specifically comprises the following steps: collecting related data of a cement pavement; a finite element numerical calculation method is adopted to construct an old cement concrete pavement fracturing model, specifically, a bidirectional contact unit is adopted to simulate the occlusion state of cracks at the fractured position of the old cement concrete pavement, and the influence of the elastic coefficient of the bidirectional contact unit and the fractured cement concrete slab bottom supporting condition on the shear deformation of the cracks at the fractured position is analyzed; and a composite model of the fractured old cement concrete pavement and the asphalt overlay layer is constructed, and the state of the asphalt overlay layer is obtained by calculating the fatigue life and allowable shear stress of the asphalt overlay layer on the fractured crack. According to the method, the state of the asphalt overlay can be accurately estimated through a full-chain quantitative model of crack occlusion-base deformation-asphalt shear stress-fatigue life.

Description

Technical Field

[0001] The present invention relates to the technical field of road safety detection, and in particular to a method for estimating the state of an asphalt overlay layer based on the fracturing state of a cement pavement. Background Art

[0002] When renovating old cement concrete pavements, asphalt overlays can significantly improve comfort. They also offer advantages such as full utilization of the existing pavement structure, low cost, and minimal traffic disruption, leading to their widespread application. However, asphalt overlays are prone to reflective cracking at the joints of the original cement pavement during use, seriously impacting the service life of the overlay. Therefore, controlling reflective cracking is a crucial factor in the design of asphalt overlays. Repeated load action is a major cause of reflective cracking. During load action, excessive shear deformation of the slab edges at the joints or compression cracks in the original cement pavement leads to excessive stress on the bottom surface of the asphalt layer, causing cracking. The cracks then propagate toward the surface of the overlay, forming surface cracks. To address this failure mode of asphalt overlays, design should prioritize controlling shear deformation at the joints of the original cement pavement. Cracking and stabilizing old cement concrete pavements during renovation can reduce stress concentration at the original joints. While significant attention is paid to shear and overall deformation at the joints or compression cracks in the original pavement, previously proposed shear deformation indices or formulas are often empirical and difficult to adapt to the varying conditions of pavement structure. Therefore, the present invention proposes a method for estimating the state of an asphalt overlay layer based on the fracturing state of a cement pavement to solve the above problems. Summary of the Invention

[0003] In response to the shortcomings of the existing technology, the present invention develops a method for predicting the state of asphalt overlay based on the fracturing state of cement pavement. By constructing a fracturing model of the old cement concrete pavement and a composite model of the asphalt overlay of the cement pavement, the shear deformation at the fracturing cracks of the cement pavement and the shear stress at the bottom of the asphalt overlay at the fracturing cracks of the old cement pavement are analyzed. The state of the asphalt overlay can be better predicted according to the fracturing state of the cement pavement.

[0004] The technical solution to the technical problem of the present invention is a method for estimating the state of an asphalt overlay layer based on the fracturing state of a cement pavement, comprising the following steps: S1. Collect relevant data of cement pavement; S2. A finite element numerical calculation method was used to construct a model of the compression fracture of an old cement concrete pavement. Specifically, a bidirectional contact element was used to simulate the occlusal state of the cracks at the compression fracture site of the old cement concrete pavement. The effects of the elastic coefficient of the bidirectional contact element and the bottom support of the fractured cement concrete slab on the shear deformation of the fractured cracks were analyzed. S3. Construct a composite model of the old cement concrete pavement and the asphalt overlay after fracturing, and obtain the state of the asphalt overlay by calculating the fatigue life and allowable shear stress of the asphalt overlay on the cracks at the fracturing location.

[0005] S1 is as follows: The relevant data of cement pavement are specifically data of old cement concrete pavement in a fracturing state, which are used to construct a fracturing model of old cement concrete pavement; The data used to construct the fracturing model of old cement concrete pavement include elastic modulus, and the corresponding Poisson's ratio is determined based on the measured elastic modulus; The data used to construct the old cement concrete pavement cracking model also include the length and width of the cracked cement concrete slab; The data used to construct the old cement concrete pavement cracking model also include foundation depth, applied load, and wheel load ground contact shape.

[0006] Based on the collected cement pavement data, the finite element numerical calculation method is used to construct the fracturing model of the old cement concrete pavement. The specific operations are as follows: Apply full constraint boundary conditions to the bottom surface of the old cement concrete pavement fracture model so that the displacement of the model in all directions is zero; Free boundary conditions are imposed on the side of the old cement concrete pavement fracture model, so that the displacement of the side nodes in all directions is unrestricted; The degrees of freedom of the top surface nodes of the old cement concrete pavement cracking model are kept open.

[0007] The specific operation process of establishing the fracturing model of old cement concrete pavement using the finite element numerical calculation method is as follows: (1) Establish components or models: Create geometric components or overall models based on actual engineering requirements to determine the length, width, and foundation depth of the fractured old cement concrete slab; (2) Assigning material properties: Assigning corresponding material properties to each component in the model, including the thickness, elastic modulus, Poisson's ratio and density of the fractured cement concrete slab; (3) Contact setting: Determine the contact type, friction coefficient, and constraint relationship between the fractured cement concrete road and the asphalt overlay; (4) Boundary conditions and loads: Set boundary conditions: Set the bottom of the model to be completely fixed, set the lateral constraints of the model to impose symmetric boundary conditions; Determine loads: Determine applied loads and wheel load contact geometry; (5) Meshing and post-processing: Determine the mesh type and then perform mesh division; Identify key results for post-processing; (6) Analyze the shear deformation of the cracks at the fracturing site.

[0008] The bidirectional contact element is used to simulate the occlusal state of cracks at the compression fracture of the old cement concrete pavement. The specific operation is as follows: Multiple bidirectional contact units are set at the fractures to be fractured. The elastic coefficients of the bidirectional contact units are adjusted according to the actual fracture occlusion state. By controlling the elastic coefficients of the bidirectional contact units, the mechanical behavior under different fracture occlusion states is simulated. The load is applied at the wheel load location, and the local mesh is encrypted at the load application location. The mesh is refined at the cracks of the fractured cement concrete slab and the nearby asphalt overlay location.

[0009] The process of constructing a composite model of the old cement concrete pavement after fracturing and the asphalt overlay is as follows: Assuming that the interlayer characteristics between the asphalt overlay and the old cement concrete pavement after fracturing are completely continuous, the overlay asphalt layer is directly added to the fracturing model of the old cement concrete pavement to obtain a composite model of the old cement concrete pavement after fracturing and the asphalt overlay. The elastic modulus of the asphalt overlay is measured, and the corresponding Poisson's ratio is calculated.

[0010] The state of the asphalt overlay is predicted based on the composite model of the old cement concrete pavement and the asphalt overlay after fracturing. The specific operation is as follows: (1) Calculate the shear force between the cracks at the fracturing location, and determine the interlocking and coordinated force transmission capacity between the cracks based on the shear force between the cracks at the fracturing location; The shear force between cracks is the stress acting on the crack surface perpendicular to the crack propagation direction. The bite-cooperation force transmission capacity between cracks at the fracturing site is the ability of concrete aggregates to resist crack propagation through mutual bite and friction. The shear force between cracks at the fracturing site is equivalent to the bite-cooperation force transmission capacity between cracks. The calculation formula for the shear force between cracks is as follows: , in, Indicates the shear force between the cracks at the fracturing site, that is, the bite-coordinated force transmission capacity between the cracks; represents the initial shear strength; Indicates the maximum effective crack width; represents the friction coefficient; represents the normal stress; Indicates the actual crack width; (2) The elastic coefficient of the bidirectional contact unit is determined according to the bite-cooperative force transmission capacity between the cracks at the fracturing site. Multiple bidirectional contact units are set at the cracks of the fractured cement concrete slab. The bite-cooperative force transmission capacity between the cracks is simulated by controlling the elastic coefficient of the bidirectional contact unit. The width of the fractured cement concrete slab is set to , the thickness is set to , and divide the thickness into nodes, assuming that the width of the inter-plate crack is zero, the relationship between the elastic coefficient of the bidirectional contact element and the bite-cooperative force transmission capacity between the cracks is as follows: , , in, Represents the elastic coefficient of the bidirectional contact element; Indicates the shear displacement difference of the corresponding nodes on both sides of the fracture at the fracturing location; Indicates the shear strain between cracks at the fracturing location; The elastic coefficient of the bidirectional contact unit is obtained from the relationship between the elastic coefficient of the bidirectional contact unit and the bite cooperative force transmission ability between the cracks at the fracturing position. , the calculation formula is as follows: , in, represents the shear modulus of the material, represents the Young's modulus of the material; (3) Use a dynamic deflection meter to measure the deflection curve under load in the plate and calculate the equivalent rebound modulus of the base layer , the shear deformation on both sides of the fracturing crack is evaluated based on the elastic coefficient of the bidirectional contact element and the equivalent rebound modulus of the base layer. The calculation formula is as follows: , ; in, represents the shear deformation on both sides of the crack, represents the load diffusion coefficient of the pavement structure, Indicates the deformation value at the load center; (4) When adding asphalt overlays of different thicknesses, the effect of the change in the crack's synergistic force transmission performance on the shear stress of the asphalt overlay is calculated. When the crack's synergistic force transmission performance is poor, the shear stress at the crack increases significantly. Therefore, the focus is on analyzing the change law of the shear stress at the bottom of the asphalt overlay under different force transmission performance of the old cement pavement's fracturing cracks. / (1+ ); in, It represents the vertical shear stress at the bottom of the asphalt overlay layer; When the shear crack surface at the bottom of the asphalt layer is in the vertical direction, the direction of the crack surface and the vertical shear stress are consistent. Replace the shear stress in the structure ; (5) Shear deformation index of old cement pavement cracks: When calculating shear strength using the Mohr-Coulomb strength theory, limit the shear stress within the asphalt overlay structure. Not exceeding the shear strength of the structural material ,Right now , calculate the shear strength according to Coulomb theory, , Indicates the normal stress on the surface where the structural layer may fail. and are the cohesion and internal friction angle of the material respectively; Shear stress level of asphalt overlay obtained from shear fatigue test and ultimate shear stress , the shear fatigue equation is obtained by linear fitting, and the calculation formula is as follows: , in, Indicates the number of fatigue times; According to the fatigue times and ultimate shear stress Calculation of allowable shear strength , ; Comparing shear stresses within structures , shear strength of structural layer materials and allowable shear strength , judge the status of the asphalt overlay: when When the asphalt overlay is damaged immediately, there is a risk of damage; when When , the asphalt overlay is in the fatigue damage accumulation stage; when When the asphalt overlay is in a safe state.

[0011] The effects provided in the summary of the invention are only the effects of the embodiments, rather than all the effects of the invention. The above technical solution has the following advantages or beneficial effects: The present invention constructs a fracturing model of an old cement concrete pavement through a finite element numerical calculation method, uses a bidirectional contact unit to simulate the bite state of cracks at the fracturing location of the old cement concrete pavement, studies the shear deformation variation law of cracks at the fracturing location under different bidirectional contact unit elastic coefficients and the bottom support of the fracturing cement concrete slab, calculates the fatigue life and allowable shear stress of the asphalt overlay layer on the crack at the fracturing location by constructing a composite model of the old cement concrete pavement and the asphalt overlay layer after fracturing, and further analyzes the composite force relationship between the fracturing of the cement concrete pavement and the asphalt overlay layer; specifically, by systematically analyzing the correlation between the shear deformation and shear stress of the crack, combined with the Mohr-Coulomb strength theory, and taking the shear stress at the bottom of the overlay layer not exceeding the allowable shear strength of the material as the control condition, finally proposes a joint crack shear deformation evaluation index suitable for old road reconstruction, which can provide a theoretical basis for the quantitative evaluation of the load transfer performance of the joint in the asphalt overlay project; The present invention confirms the quantitative influence of the bite-coordinated force transmission state of the old cement slab fracturing cracks and the foundation support conditions on the shear deformation of the fracturing cracks, filling the gap in the existing research on the comprehensive consideration of crack bite and comprehensive foundation support state. Based on the research results, the shear stress of the overlay layer at the fracturing cracks of the old cement slabs can be deeply analyzed, and then the fatigue life of the asphalt overlay layer can be analyzed. Finally, based on the fatigue life of the asphalt overlay layer, the shear deformation standard of the cement pavement fracturing cracks and the shear stress state evaluation of the asphalt overlay layer are established.

[0012] Therefore, the present invention provides specific and operational parameters for the design of cement concrete pavement fracturing reconstruction, which can help engineers more accurately predict and control the shear deformation of cement slab fracturing cracks and the stress state assessment of asphalt overlay layers during the design phase, thereby increasing the service life of the pavement and reducing maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0014] Figure 1 Schematic diagram of the method of the present invention. DETAILED DESCRIPTION

[0015] In order to clearly illustrate the technical features of this solution, the present invention is described in detail below through specific implementation methods and in conjunction with the accompanying drawings.

[0016] Example 1 like Figure 1 As shown in FIG, a method for estimating the state of asphalt overlay based on the fracturing state of cement pavement is provided, and the steps are as follows: S1. Collect relevant data of cement pavement; S2. A finite element numerical calculation method was used to construct a model of the compression fracture of an old cement concrete pavement. Specifically, a bidirectional contact element was used to simulate the occlusal state of the cracks at the compression fracture site of the old cement concrete pavement. The effects of the elastic coefficient of the bidirectional contact element and the bottom support of the fractured cement concrete slab on the shear deformation of the fractured cracks were analyzed. S3. Construct a composite model of the old cement concrete pavement and the asphalt overlay after fracturing, and obtain the state of the asphalt overlay by calculating the fatigue life and allowable shear stress of the asphalt overlay on the cracks at the fracturing location.

[0017] In a specific implementation manner, S1 is specifically as follows: The relevant data of cement pavement are specifically data of old cement concrete pavement in a fracturing state, which are used to construct a fracturing model of old cement concrete pavement; The data used to construct the fracturing model of old cement concrete pavement include elastic modulus, and the corresponding Poisson's ratio is determined based on the measured elastic modulus; The data used to construct the old cement concrete pavement cracking model also include the length and width of the cracked cement concrete slab; The data used to construct the old cement concrete pavement cracking model also include foundation depth, applied load, and wheel load ground contact shape.

[0018] In a specific implementation, based on the collected cement pavement data, a finite element numerical calculation method is used to construct a fracturing model of an old cement concrete pavement. The specific operations are as follows: Apply full constraint boundary conditions to the bottom surface of the old cement concrete pavement fracture model so that the displacement of the model in all directions is zero; Free boundary conditions are imposed on the side of the old cement concrete pavement fracture model, so that the displacement of the side nodes in all directions is unrestricted; The degrees of freedom of the top surface nodes of the old cement concrete pavement cracking model are kept open.

[0019] Since the model has high requirements on the quality of input data, the present invention selects a high-precision detector for data acquisition.

[0020] In a specific embodiment, the operation process of establishing the fracturing model of the old cement concrete pavement using the finite element numerical calculation method is as follows: (1) Establish components or models: Create geometric components or overall models based on actual engineering requirements to determine the length, width, and foundation depth of the fractured old cement concrete slab; (2) Assigning material properties: Assigning corresponding material properties to each component in the model, including the thickness, elastic modulus, Poisson's ratio and density of the fractured cement concrete slab; (3) Contact setting: Determine the contact type, friction coefficient, and constraint relationship between the fractured cement concrete road and the asphalt overlay; (4) Boundary conditions and loads: Set boundary conditions: Set the bottom of the model to be completely fixed, set the lateral constraints of the model to impose symmetric boundary conditions; Determine loads: Determine applied loads and wheel load contact geometry; (5) Meshing and post-processing: Determine the mesh type and then perform mesh division; Identify key results for post-processing; (6) Analyze the shear deformation of the cracks at the fracturing site.

[0021] In a specific embodiment, the bidirectional contact unit is used to simulate the occlusal state of cracks at the compression fracture of the old cement concrete pavement. The specific operation is as follows: Multiple bidirectional contact units are set at the fractures to be fractured. The elastic coefficients of the bidirectional contact units are adjusted according to the actual fracture occlusion state. By controlling the elastic coefficients of the bidirectional contact units, the mechanical behavior under different fracture occlusion states is simulated. The load is applied at the wheel load location, and the local mesh is encrypted at the load application location. The mesh is refined at the cracks of the fractured cement concrete slab and the nearby asphalt overlay location.

[0022] In a specific embodiment, the process of constructing a composite model of the old cement concrete pavement after fracturing and the asphalt overlay is as follows: Assuming that the interlayer characteristics between the asphalt overlay and the old cement concrete pavement after fracturing are completely continuous, the overlay asphalt layer is directly added to the fracturing model of the old cement concrete pavement to obtain a composite model of the old cement concrete pavement after fracturing and the asphalt overlay. The elastic modulus of the asphalt overlay is measured, and the corresponding Poisson's ratio is calculated.

[0023] In a specific embodiment, the state of the asphalt overlay is predicted based on the composite model of the old cement concrete pavement after fracturing and the asphalt overlay. The specific operations are as follows: (1) Calculate the shear force between the cracks at the fracturing location, and determine the interlocking and coordinated force transmission capacity between the cracks based on the shear force between the cracks at the fracturing location; The shear force between cracks is the stress acting on the crack surface perpendicular to the crack propagation direction. The bite-cooperation force transmission capacity between cracks at the fracturing site is the ability of concrete aggregates to resist crack propagation through mutual bite and friction. The shear force between cracks at the fracturing site is equivalent to the bite-cooperation force transmission capacity between cracks. The calculation formula for the shear force between cracks is as follows: , in, Indicates the shear force between the cracks at the fracturing site, that is, the bite-coordinated force transmission capacity between the cracks; Indicates initial shear strength, initial shear strength It can be obtained by direct shear test; Indicates the maximum effective crack width; represents the friction coefficient, Determined according to the properties and surface roughness of concrete aggregate; represents the normal stress; Indicates the actual crack width; (2) The elastic coefficient of the bidirectional contact unit is determined according to the bite-cooperative force transmission capacity between the cracks at the fracturing site. Multiple bidirectional contact units are set at the cracks of the fractured cement concrete slab. The bite-cooperative force transmission capacity between the cracks is simulated by controlling the elastic coefficient of the bidirectional contact unit. The width of the fractured cement concrete slab is set to , the thickness is set to , and divide the thickness into nodes, assuming that the width of the inter-plate crack is zero, the relationship between the elastic coefficient of the bidirectional contact element and the bite-cooperative force transmission capacity between the cracks is as follows: , , in, Represents the elastic coefficient of the bidirectional contact element; Indicates the shear displacement difference of the corresponding nodes on both sides of the fracture at the fracturing location; Indicates the shear strain between cracks at the fracturing location; The elastic coefficient of the bidirectional contact unit is obtained from the relationship between the elastic coefficient of the bidirectional contact unit and the bite cooperative force transmission ability between the cracks at the fracturing position. , the calculation formula is as follows: , in, represents the shear modulus of the material, represents the Young's modulus of the material; (3) Use a dynamic deflection meter to measure the deflection curve under load in the plate and calculate the equivalent rebound modulus of the base layer , the shear deformation on both sides of the fracturing crack is evaluated based on the elastic coefficient of the bidirectional contact element and the equivalent rebound modulus of the base layer. The calculation formula is as follows: , ; in, represents the shear deformation on both sides of the crack, represents the load diffusion coefficient of the pavement structure, Indicates the deformation value at the load center; (4) When adding asphalt overlays of different thicknesses, the effect of the change in the crack's synergistic force transmission performance on the shear stress of the asphalt overlay is calculated. When the crack's synergistic force transmission performance is poor, the shear stress at the crack increases significantly. Therefore, the focus is on analyzing the change law of the shear stress at the bottom of the asphalt overlay under different force transmission performance of the old cement pavement's fracturing cracks. / (1+ ); in, It represents the vertical shear stress at the bottom of the asphalt overlay layer; When the shear crack surface at the bottom of the asphalt layer is in the vertical direction, the direction of the crack surface and the vertical shear stress are consistent. Replace the shear stress in the structure ; (5) Shear deformation index of old cement pavement cracks: When calculating shear strength using the Mohr-Coulomb strength theory, limit the shear stress within the asphalt overlay structure. Not exceeding the shear strength of the structural material ,Right now , calculate the shear strength according to Coulomb theory, , Indicates the normal stress on the surface where the structural layer may fail. and are the cohesion and internal friction angle of the material respectively; Shear stress level of asphalt overlay obtained from shear fatigue test and ultimate shear stress , the shear fatigue equation is obtained by linear fitting, and the calculation formula is as follows: , in, Indicates the number of fatigue times; According to the fatigue times and ultimate shear stress Calculation of allowable shear strength , ; Comparing shear stresses within structures , shear strength of structural layer materials and allowable shear strength , judge the status of the asphalt overlay: when When the asphalt overlay is damaged immediately, there is a risk of damage; when When , the asphalt overlay is in the fatigue damage accumulation stage; when When the asphalt overlay is in a safe state.

[0024] Example 2 In order to better demonstrate the technical effect of the present invention, according to the finite element numerical calculation results, by setting the elastic coefficient of the bidirectional contact unit at different joints , the wheel load was 100KN, the size was 22cm×16cm, and the horizontal normal stress, shear stress and crack shear deformation index of the bottom of the asphalt overlay layer were measured. According to the Coulomb strength theory, the ultimate shear strength and allowable shear strength of the bottom of the asphalt overlay layer were calculated. The crack shear deformation index is based on the equivalent rebound modulus of the bottom foundation of the slab. and the required fatigue cracking number N, the results under different conditions are shown in Table 1; Table 1 Calculation results of ultimate shear strength and allowable shear strength of asphalt overlay bottom The ultimate shear strength and allowable shear strength data of the asphalt overlay bottom are converted into a curve. The crack shear deformation index corresponding to the intersection of the two is the crack shear deformation that reaches the fatigue life of this allowable shear strength curve. The crack shear deformation index corresponding to N = 1000 and N = 5000 under different equivalent rebound moduli are shown in Table 2. Table 2 Crack shear deformation index The process of estimating the status of the asphalt overlay based on the above results is as follows: (1) Determine parameters: Determine the equivalent rebound modulus Et of the slab foundation and the required number of fatigue cracking times N; (2) Lookup table: Find the corresponding crack shear deformation standard in the table according to the determined equivalent rebound modulus Et and the required fatigue cracking number N; (3) Linear interpolation: If the values ​​of Et and N are not directly given in the table, linear interpolation is required to estimate the crack shear deformation; (4) Comparison: Compare the calculated or table-based crack shear deformation value with the actual measured crack shear deformation value. If the actual crack shear deformation value exceeds the standard value given in the table, the structure or pavement needs to be reinforced or maintained.

[0025] The crack shear deformation index can be obtained by linear interpolation in the table based on the equivalent rebound modulus of the slab bottom foundation and the required number of fatigue cracking times. If the deflection difference during different fatigue cracking loads is below the standard value, it means that the asphalt overlay layer is in good condition at this time; when the shear deformation value is greater than the standard value, it means that the asphalt overlay layer at this time does not meet normal use and needs maintenance.

[0026] Although the above describes the specific implementation methods of the invention in conjunction with the accompanying drawings, it does not limit the scope of protection of the invention. Based on the technical solution of the present invention, various modifications or variations that can be made by those skilled in the art without creative work are still within the scope of protection of the present invention.

Claims

1. A method for estimating the state of an asphalt overlay layer based on the fracturing state of a cement pavement, characterized by the following steps: as follows: S1. Collect relevant data of cement pavement; S2. A finite element numerical calculation method was used to construct a model of the compression fracture of an old cement concrete pavement. Specifically, a bidirectional contact element was used to simulate the occlusal state of the cracks at the compression fracture site of the old cement concrete pavement. The effects of the elastic coefficient of the bidirectional contact element and the bottom support of the fractured cement concrete slab on the shear deformation of the fractured cracks were analyzed. S3. Construct a composite model of the old cement concrete pavement and the asphalt overlay after fracturing, and obtain the state of the asphalt overlay by calculating the fatigue life and allowable shear stress of the asphalt overlay on the cracks at the fracturing location.

2. The method for estimating the state of an asphalt overlay layer based on the fracturing state of a cement pavement according to claim 1, wherein: S1 is as follows: The relevant data of cement pavement are specifically data of old cement concrete pavement in a fracturing state, which are used to construct a fracturing model of old cement concrete pavement; The data used to construct the fracturing model of old cement concrete pavement include elastic modulus, and the corresponding Poisson's ratio is determined based on the measured elastic modulus; The data used to construct the old cement concrete pavement cracking model also include the length and width of the cracked cement concrete slab; The data used to construct the old cement concrete pavement cracking model also include foundation depth, applied load, and wheel load ground contact shape.

3. The method for estimating the state of an asphalt overlay layer based on the fracturing state of a cement pavement according to claim 2, wherein: Based on the collected cement pavement data, the finite element numerical calculation method is used to construct the fracturing model of the old cement concrete pavement. The specific operations are as follows: Apply full constraint boundary conditions to the bottom surface of the old cement concrete pavement fracture model so that the displacement of the model in all directions is zero; Free boundary conditions are imposed on the side of the old cement concrete pavement fracture model, so that the displacement of the side nodes in all directions is unrestricted; The degrees of freedom of the top surface nodes of the old cement concrete pavement cracking model are kept open.

4. The method for estimating the state of an asphalt overlay layer based on the fracturing state of a cement pavement according to claim 3 is characterized in that: The specific operation process of establishing the fracturing model of old cement concrete pavement using the finite element numerical calculation method is as follows: (1) Establish components or models: Create geometric components or overall models based on actual engineering requirements to determine the length, width, and foundation depth of the fractured old cement concrete slab; (2) Assigning material properties: Assigning corresponding material properties to each component in the model, including the thickness, elastic modulus, Poisson's ratio and density of the fractured cement concrete slab; (3) Contact setting: Determine the contact type, friction coefficient, and constraint relationship between the fractured cement concrete road and the asphalt overlay; (4) Boundary conditions and loads: Set boundary conditions: Set the bottom of the model to be completely fixed, set the lateral constraints of the model to impose symmetric boundary conditions; Determine loads: Determine applied loads and wheel load contact geometry; (5) Meshing and post-processing: Determine the mesh type and then perform mesh division; Identify key results for post-processing; (6) Analyze the shear deformation of the cracks at the fracturing site.

5. The method for estimating the state of an asphalt overlay layer based on the fracturing state of a cement pavement according to claim 4 is characterized in that: The bidirectional contact element is used to simulate the occlusal state of cracks at the compression fracture of the old cement concrete pavement. The specific operation is as follows: Multiple bidirectional contact units are set at the fractures to be fractured. The elastic coefficients of the bidirectional contact units are adjusted according to the actual fracture occlusion state. By controlling the elastic coefficients of the bidirectional contact units, the mechanical behavior under different fracture occlusion states is simulated. The load is applied at the wheel load location, and the local mesh is encrypted at the load application location. The mesh is refined at the cracks of the fractured cement concrete slab and the nearby asphalt overlay location.

6. The method for estimating the state of an asphalt overlay layer based on the fracturing state of a cement pavement according to claim 5, wherein: The process of constructing a composite model of the old cement concrete pavement after fracturing and the asphalt overlay is as follows: Assuming that the interlayer characteristics between the asphalt overlay and the old cement concrete pavement after fracturing are completely continuous, the overlay asphalt layer is directly added to the fracturing model of the old cement concrete pavement to obtain a composite model of the old cement concrete pavement after fracturing and the asphalt overlay. The elastic modulus of the asphalt overlay is measured, and the corresponding Poisson's ratio is calculated.

7. The method for estimating the state of an asphalt overlay layer based on the fracturing state of a cement pavement according to claim 6, wherein: The state of the asphalt overlay is predicted based on the composite model of the old cement concrete pavement and the asphalt overlay after fracturing. The specific operation is as follows: (1) Calculate the shear force between the cracks at the fracturing location, and determine the interlocking and coordinated force transmission capacity between the cracks based on the shear force between the cracks at the fracturing location; The shear force between cracks is the stress acting on the crack surface perpendicular to the crack propagation direction. The bite-cooperation force transmission capacity between cracks at the fracturing site is the ability of concrete aggregates to resist crack propagation through mutual bite and friction. The shear force between cracks at the fracturing site is equivalent to the bite-cooperation force transmission capacity between cracks. The calculation formula for the shear force between cracks is as follows: ， in, Indicates the shear force between the cracks at the fracturing site, that is, the bite-coordinated force transmission capacity between the cracks; represents the initial shear strength; Indicates the maximum effective crack width; represents the friction coefficient; represents the normal stress; Indicates the actual crack width; (2) The elastic coefficient of the bidirectional contact unit is determined according to the bite-cooperative force transmission capacity between the cracks at the fracturing site. Multiple bidirectional contact units are set at the cracks of the fractured cement concrete slab. The bite-cooperative force transmission capacity between the cracks is simulated by controlling the elastic coefficient of the bidirectional contact unit. The width of the fractured cement concrete slab is set to , the thickness is set to , and divide the thickness into nodes, assuming that the width of the inter-plate crack is zero, the relationship between the elastic coefficient of the bidirectional contact element and the bite-cooperative force transmission capacity between the cracks is as follows: ， ， in, Represents the elastic coefficient of the bidirectional contact element; Indicates the shear displacement difference of the corresponding nodes on both sides of the fracture at the fracturing location; Indicates the shear strain between cracks at the fracturing location; The elastic coefficient of the bidirectional contact unit is obtained from the relationship between the elastic coefficient of the bidirectional contact unit and the bite cooperative force transmission ability between the cracks at the fracturing position. , the calculation formula is as follows: ， in, represents the shear modulus of the material, represents the Young's modulus of the material; (3) Use a dynamic deflection meter to measure the deflection curve under load in the plate and calculate the equivalent rebound modulus of the base layer , the shear deformation on both sides of the fracturing crack is evaluated based on the elastic coefficient of the bidirectional contact element and the equivalent rebound modulus of the base layer. The calculation formula is as follows: ， ； in, represents the shear deformation on both sides of the crack, represents the load diffusion coefficient of the pavement structure, Indicates the deformation value at the load center; (4) When adding asphalt overlays of different thicknesses, the effect of the change in the crack's synergistic force transmission performance on the shear stress of the asphalt overlay is calculated. When the crack's synergistic force transmission performance is poor, the shear stress at the crack increases significantly. Therefore, the focus is on analyzing the change law of the shear stress at the bottom of the asphalt overlay under different force transmission performance of the old cement pavement's fracturing cracks. / (1+ )； in, It represents the vertical shear stress at the bottom of the asphalt overlay layer; When the shear crack surface at the bottom of the asphalt layer is in the vertical direction, the direction of the crack surface and the vertical shear stress are consistent. Replace the shear stress in the structure ; (5) Shear deformation index of old cement pavement cracks: When calculating shear strength using the Mohr-Coulomb strength theory, limit the shear stress within the asphalt overlay structure. Not exceeding the shear strength of the structural material ,Right now , calculate the shear strength according to Coulomb theory, , Indicates the normal stress on the surface where the structural layer may fail. and are the cohesion and internal friction angle of the material respectively; Shear stress level of asphalt overlay obtained from shear fatigue test and ultimate shear stress , the shear fatigue equation is obtained by linear fitting, and the calculation formula is as follows: ， in, Indicates the number of fatigue times; According to the fatigue times and ultimate shear stress Calculation of allowable shear strength , ; Comparing shear stresses within structures , shear strength of structural layer materials and allowable shear strength , judge the status of the asphalt overlay: when When the asphalt overlay is damaged immediately, there is a risk of damage; when When , the asphalt overlay is in the fatigue damage accumulation stage; when When the asphalt overlay is in a safe state.

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