An asphalt overlay layer state estimation method based on cement pavement fracturing state

Abstract

The present application relates to the technical field of road safety detection, in particular to a kind of asphalt overlay state estimation method based on cement pavement fracturing state, specifically as follows: relevant data of cement pavement is collected;Old cement concrete pavement fracturing model is constructed using finite element numerical calculation method, specifically using two-way contact element to simulate the engagement state of crack at old cement concrete pavement fracturing, the influence of two-way contact element elastic coefficient and the bottom support condition of fracturing cement concrete slab on the shear deformation of crack at fracturing is analyzed;The composite model of old cement concrete pavement and asphalt overlay after fracturing is constructed, and the state of asphalt overlay is obtained by calculating the fatigue life and allowable shear stress of asphalt overlay on the crack at fracturing.The present application can accurately estimate the state of asphalt overlay through the whole-chain quantitative model of "crack engagement→subgrade deformation→asphalt shear stress→fatigue life".

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of road safety detection, and particularly relates to a method for estimating the state of an asphalt overlay layer based on the cracking state of a cement pavement. BACKGROUND

[0002] When reconstructing an old cement concrete pavement, an asphalt overlay structure can significantly improve the comfort of the old cement concrete pavement, and has the advantages of fully utilizing the original pavement structure, low cost, and less impact on traffic, and therefore is widely used. However, during the use of the asphalt overlay structure, reflection cracks are easily generated at the joints of the original cement pavement, which seriously affects the service life of the overlay layer. Therefore, the control of reflection cracks is an important index in the design of the asphalt overlay layer. The repeated action of load is an important inducement for the generation of reflection cracks. During the action of the load, the excessive shear deformation of the slab edges on both sides of the joint or the cracking crack of the original cement pavement leads to excessive stress on the bottom surface of the asphalt layer and causes cracking, and then the crack expands to the surface of the overlay layer to form a surface crack. In view of this damage mode of the asphalt overlay layer, the focus of the design should be placed on the control of the shear deformation of the joint of the original cement pavement. When reconstructing the old cement concrete pavement, cracking and pressure stabilization of the old cement concrete pavement can reduce the stress concentration phenomenon at the original joint. Although enough attention is paid to the shear deformation and overall deformation of the original pavement joint or the cracking crack, the shear deformation index or formula proposed in the past is mostly empirical and is difficult to adapt to various situations of the pavement structure.

[0003] Therefore, the present application provides a method for estimating the state of an asphalt overlay layer based on the cracking state of a cement pavement to solve the above problems. SUMMARY

[0004] The present application is developed to solve the problems of the prior art, and provides a method for estimating the state of an asphalt overlay layer based on the cracking state of a cement pavement. The old cement concrete pavement cracking model and the cement pavement asphalt overlay layer composite model are constructed, the shear deformation at the cracking crack of the cement pavement and the shear stress at the bottom of the asphalt overlay layer at the cracking crack of the old cement pavement are analyzed, and the state of the asphalt overlay layer can be better estimated according to the cracking state of the cement pavement.

[0005] The technical scheme for solving the technical problem of the present application is a method for estimating the state of an asphalt overlay layer based on the cracking state of a cement pavement, which comprises the following steps:

[0006] S1, collecting relevant data of the cement pavement;

[0007] S2, constructing an old cement concrete pavement cracking model by using a finite element numerical calculation method, specifically simulating the biting state of the cracking crack at the old cement concrete pavement cracking by using a bidirectional contact element, and analyzing the influence of the elastic coefficient of the bidirectional contact element and the support condition of the cracking cement concrete slab bottom on the shear deformation at the cracking crack;

[0008] S3, build a composite model of the old cement concrete pavement after fracturing and the asphalt overlay, and obtain the state of the asphalt overlay by calculating the fatigue life and allowable shear stress of the asphalt overlay on the fracture.

[0009] S1 is specifically as follows:

[0010] The related data of the cement pavement is specifically data of the old cement concrete pavement in the fracturing state, and is used for building a fracturing model of the old cement concrete pavement;

[0011] The data for building the fracturing model of the old cement concrete pavement includes the elastic modulus, and the corresponding Poisson's ratio is determined according to the measured elastic modulus;

[0012] The data for building the fracturing model of the old cement concrete pavement also includes the length and width of the fractured cement concrete slab;

[0013] The data for building the fracturing model of the old cement concrete pavement also includes the foundation depth, applied load, and wheel load ground shape.

[0014] Based on the collected related data of the cement pavement, a fracturing model of the old cement concrete pavement is built by using a finite element numerical calculation method, and the specific operation is as follows:

[0015] Full constraint boundary conditions are applied to the bottom surface of the fracturing model of the old cement concrete pavement, so that the displacement of the model in each direction is zero;

[0016] Free boundary conditions are applied to the side surface of the fracturing model of the old cement concrete pavement, so that the displacement of the side surface nodes in each direction is not limited;

[0017] The degrees of freedom of the top surface nodes of the fracturing model of the old cement concrete pavement are kept open.

[0018] The operation process of using the finite element numerical calculation method to build the fracturing model of the old cement concrete pavement is specifically as follows:

[0019] (1) Establish components or models: according to the actual engineering requirements, create geometric components or overall models, and determine the length, width of the fractured old cement concrete slab, and the foundation depth;

[0020] (2) Assign material properties: specify the corresponding material properties for each component in the model, including the thickness, elastic modulus, Poisson's ratio and density of the fractured cement concrete slab;

[0021] (3) Contact setting: determine the contact type, friction coefficient and constraint relationship of the fractured cement concrete road and the asphalt overlay;

[0022] (4) Boundary conditions and loads:

[0023] Set boundary conditions: set the bottom of the model completely fixed, set the model lateral constraint to apply symmetric boundary conditions;

[0024] Determine the load: determine the applied load and the wheel load ground shape;

[0025] (5) meshing and post-processing:

[0026] Determine the grid type, then meshing;

[0027] Determine the key results of post-processing;

[0028] (6) analyze the shear deformation of the fracture at the cracking site.

[0029] The biting state of the fracture at the cracking site of the old cement concrete pavement is simulated by the two-way contact element, and the specific operation is as follows:

[0030] A plurality of two-way contact elements are arranged at the cracking site, the size of the elastic coefficient of the two-way contact element is adjusted according to the biting state of the actual fracture, and the mechanical behavior under different fracture biting states is simulated by controlling the elastic coefficient of the two-way contact element;

[0031] The load is applied at the wheel load position, and the local mesh is encrypted at the load position, and the mesh is refined at the fracture site and the position of the asphalt overlay layer near the cracked cement slab.

[0032] The process of constructing the composite model of the cracked old cement concrete pavement and the asphalt overlay layer is as follows:

[0033] Assuming that the interlayer properties between the asphalt overlay layer and the cracked old cement concrete pavement are in a completely continuous state, the composite model of the cracked old cement concrete pavement and the asphalt overlay layer is obtained by directly adding the overlay asphalt layer to the cracking model of the old cement concrete pavement, the elastic modulus of the asphalt overlay layer is measured, and the corresponding Poisson's ratio is calculated.

[0034] According to the composite model of the cracked old cement concrete pavement and the asphalt overlay layer, the state of the asphalt overlay layer is predicted, and the specific operation is as follows:

[0035] (1) Calculate the shear force between the fractures at the cracking site, and determine the biting and cooperative force transmission capacity between the fractures according to the shear force between the fractures at the cracking site;

[0036] The shear force between the fractures is the stress acting on the fracture surface perpendicular to the fracture propagation direction, and the biting and cooperative force transmission capacity between the fractures at the cracking site is the ability of the concrete aggregate to bite and friction to resist the expansion of the fracture, and the shear force between the fractures at the cracking site is equivalent to the biting and cooperative force transmission capacity between the fractures, and the calculation formula of the shear force between the fractures is as follows:

[0037] ,

[0038] wherein, represents the shear force between the cracks at the fracturing position, i.e., the biting and force-transferring ability between the cracks; represents the initial shear strength; represents the maximum effective crack width; represents the friction coefficient; represents the normal stress; represents the actual crack width;

[0039] (2) The elastic coefficient of the bidirectional contact unit is determined according to the biting and force-transferring ability between the cracks at the fracturing position, a plurality of bidirectional contact units are arranged at the cracks of the fractured cement concrete slab, the biting and force-transferring ability 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 the thickness is divided into nodes, the joint width between the slabs is assumed to be zero, and the relationship between the elastic coefficient of the bidirectional contact unit and the biting and force-transferring ability between the cracks is as follows:

[0040] ,

[0041] ,

[0042] wherein, represents the elastic coefficient of the bidirectional contact unit; represents the shear displacement difference of the corresponding nodes on both sides of the crack at the fracturing position; represents the shear strain between the cracks at the fracturing position;

[0043] The elastic coefficient of the bidirectional contact unit is obtained from the relationship between the elastic coefficient of the bidirectional contact unit and the biting and force-transferring ability between the cracks at the fracturing position, and the calculation formula is as follows:

[0044] ,

[0045] wherein, represents the shear modulus of the material, represents the Young's modulus of the material;

[0046] (3) The dynamic deflectometer is used to measure the deflection curve of the slab under load, and the equivalent resilient modulus of the base layer is calculated, and the shear deformation of the two sides of the fracturing crack is evaluated according to the elastic coefficient of the bidirectional contact unit and the equivalent resilient modulus of the base layer, and the calculation formula is as follows:

[0047] ,

[0048] ;

[0049] where, represents the shear deformation of the crack on both sides, represents the load diffusion coefficient of the pavement structure, represents the deformation value at the load center;

[0050] (4) When paving asphalt overlay of different thicknesses, the influence of the change of crack synergistic load transfer performance on the shear stress of asphalt overlay is calculated by trial, when the crack synergistic load transfer performance is poor, the shear stress at the crack is significantly increased, therefore, the change rule of the shear stress at the bottom of asphalt overlay under different load transfer performances of the pressure crack of old cement pavement is analyzed;

[0051] / (1+ );

[0052] where, represents the vertical shear stress at the bottom of asphalt overlay;

[0053] When the shear type cracking surface at the bottom of asphalt layer is along the vertical direction, the cracking surface and the direction of vertical shear stress are consistent, the vertical shear stress at the bottom of asphalt overlay is used to replace the shear stress in the structure;

[0054] (5) Shear deformation index of pressure crack of old cement pavement:

[0055] When checking the shear strength by using Mohr-Coulomb strength theory, the shear stress in the asphalt overlay structure is limited to not more than the shear strength of the material of the structure layer, that is, , according to the Coulomb theory, the shear strength is calculated, , represents the normal stress on the possible failure surface of the structure layer, , and are the cohesion and internal friction angle of the material, respectively; The shear stress level

[0056] and the ultimate shear stress of asphalt overlay obtained from the shear fatigue test, the shear fatigue equation is obtained by linear fitting, and the calculation formula is as follows:

[0057] ,

[0058] where, represents the number of fatigue times;

[0059] The allowable shear strength is calculated according to the number of fatigue times and the ultimate shear stress , ;​

[0060] Shear stress in the comparative structure Shear strength of the structure layer material And allowable shear strength Judge the state of the asphalt overlay:

[0061] When The asphalt overlay has an immediate risk of damage;

[0062] When The asphalt overlay is in the fatigue damage accumulation stage;

[0063] When The asphalt overlay is in a safe state.

[0064] The effects provided in the summary are only the effects of the embodiments, not all the full effects of the invention, and the above technical solutions have the following advantages or beneficial effects:

[0065] The present application constructs the old cement concrete pavement fracturing model by the finite element numerical calculation method, simulates the engagement state of the crack at the fracturing of the old cement concrete pavement by the bidirectional contact element, studies the shear deformation variation law of the crack at the fracturing under the conditions of different elastic coefficients of the bidirectional contact element and the bottom support of the fracturing cement concrete slab, calculates the fatigue life and allowable shear stress of the asphalt overlay on the crack at the fracturing by constructing the composite model of the old cement concrete pavement after fracturing and the asphalt overlay, and further analyzes the composite stress relationship between the fracturing of the cement concrete pavement and the asphalt overlay.

[0066] The present application determines the quantitative influence of the engagement and cooperative force transmission state of the fracturing crack of the old cement slab and the foundation support condition on the shear deformation of the fracturing crack, fills the gap of the existing research that comprehensively considers the engagement and comprehensive support state of the foundation, based on the research results, can deeply analyze the shear stress of the overlay at the fracturing crack of the old cement slab, and further analyze the fatigue life of the asphalt overlay, and finally establish the shear deformation standard of the fracturing crack of the cement pavement and the shear stress state evaluation of the asphalt overlay based on the fatigue life of the asphalt overlay.

[0067] Therefore, the present application provides specific and operable parameters for the fracturing reconstruction design of the cement concrete pavement, can help engineers more accurately predict and control the shear deformation of the fracturing crack of the cement slab and the stress state evaluation of the asphalt overlay in the design stage, thereby improving the service life of the pavement and reducing the maintenance cost. BRIEF DESCRIPTION OF DRAWINGS

[0068] The accompanying drawings are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and are intended to serve as an exemplification of the application, and do not limit the application.

[0069] Figure 1 The flow chart of the method of the application is shown. DETAILED DESCRIPTION

[0070] In order to clearly illustrate the technical features of the scheme, the application will be described in detail below with reference to the specific embodiments and the accompanying drawings.

[0071] Embodiment 1

[0072] As shown in the figure, a cement pavement fracturing state-based asphalt overlay state estimation method comprises the following steps: Figure 1

[0073] S1, collecting related data of the cement pavement;

[0074] S2, constructing an old cement concrete pavement fracturing model by using a finite element numerical calculation method, specifically simulating the engagement state of the cracks at the fracturing position of the old cement concrete pavement by using a bidirectional contact element, and analyzing the influence of the elastic coefficient of the bidirectional contact element and the support condition of the fracturing cement concrete slab bottom on the shear deformation of the cracks at the fracturing position.

[0075] S3, constructing a composite model of the old cement concrete pavement after fracturing and the asphalt overlay, and obtaining the state of the asphalt overlay by calculating the fatigue life and allowable shear stress of the asphalt overlay on the fracturing cracks.

[0076] In the specific embodiment, S1 is specifically as follows:

[0077] The related data of the cement pavement is specifically the data under the fracturing state of the old cement concrete pavement, which is used to construct the old cement concrete pavement fracturing model.

[0078] The data for constructing the old cement concrete pavement fracturing model includes the elastic modulus, and the corresponding Poisson's ratio is determined according to the measured elastic modulus.

[0079] The data for constructing the old cement concrete pavement fracturing model also includes the length and width of the fracturing cement concrete slab.

[0080] The data for constructing the old cement concrete pavement fracturing model also includes the foundation depth, applied load, and wheel load ground contact shape.

[0081] In the specific embodiment, based on the collected related data of the cement pavement, the old cement concrete pavement fracturing model is constructed by using the finite element numerical calculation method, and the specific operation is as follows: ​

[0082] The bottom surface of the old cement concrete pavement fracturing model is subjected to full constraint boundary conditions, so that the displacement of the model in each direction is zero;

[0083] The side surface of the old cement concrete pavement fracturing model is subjected to free boundary conditions, so that the displacement of the side surface nodes in each direction is not limited;

[0084] The top surface nodes of the old cement concrete pavement fracturing model are kept open.

[0085] Since the model has high requirements for the quality of input data, the present application selects a high-precision detector for data acquisition.

[0086] In the specific implementation, the operation process of establishing the old cement concrete pavement fracturing model using the finite element numerical calculation method is as follows:

[0087] (1) Establish components or models: according to actual engineering requirements, create geometric components or overall models, and determine the length, width of the fractured old cement concrete slab, and the foundation depth;

[0088] (2) Assign material properties: specify the corresponding material properties for each component in the model, including the thickness, elastic modulus, Poisson's ratio and density of the fractured cement concrete slab;

[0089] (3) Contact setting: determine the contact type, friction coefficient and constraint relationship of the fractured cement concrete road and the asphalt overlay;

[0090] (4) Boundary conditions and loads:

[0091] Set boundary conditions: set the bottom of the model completely fixed, and set the lateral constraint to apply symmetric boundary conditions;

[0092] Determine the load: determine the applied load and the wheel load ground shape;

[0093] (5) Meshing and post-processing:

[0094] Determine the mesh type, then perform meshing;

[0095] Determine the key results of post-processing;

[0096] (6) Analyze the shear deformation of the crack at the fracturing position.

[0097] In the specific implementation, the old cement concrete pavement fracturing crack engagement state is simulated by a two-way contact element, and the specific operation is as follows:

[0098] A plurality of bidirectional contact units are arranged at the cracks of the fractured cracks, the size of the elastic coefficient of the bidirectional contact unit is adjusted according to the actual crack biting state, and the mechanical behavior under different crack biting states is simulated by controlling the elastic coefficient of the bidirectional contact unit.

[0099] Load is applied at the wheel load, local mesh encryption processing is performed on the load application position, and mesh refinement processing is performed on the crack of the fractured cement concrete slab and the position of the asphalt overlay layer.

[0100] In the specific implementation, the process of constructing the composite model of the fractured old cement concrete pavement and the asphalt overlay layer is as follows:

[0101] Assuming that the interlayer characteristics between the asphalt overlay layer and the fractured old cement concrete pavement are in a completely continuous state, the composite model of the fractured old cement concrete pavement and the asphalt overlay layer is obtained by directly adding the overlay asphalt layer on the old cement concrete pavement fracture model, the elastic modulus of the asphalt overlay layer is measured, and the corresponding Poisson's ratio is calculated.

[0102] In the specific implementation, the state of the asphalt overlay layer is predicted according to the composite model of the fractured old cement concrete pavement and the asphalt overlay layer, and the specific operation is as follows:

[0103] (1) Calculate the shear force between the cracks at the fracture, and determine the biting and cooperative force transmission capacity between the cracks according to the shear force between the cracks at the fracture.

[0104] The shear force between the cracks is the stress perpendicular to the crack propagation direction acting on the crack surface, the biting and cooperative force transmission capacity between the cracks at the fracture is the ability of the mutual biting and friction of the concrete aggregate to resist crack propagation, the shear force between the cracks at the fracture is equivalent to the biting and cooperative force transmission capacity between the cracks, and the calculation formula of the shear force between the cracks is as follows:

[0105] ,

[0106] wherein, represents the shear force between the cracks at the fracture, that is, the biting and cooperative force transmission capacity between the cracks; represents the initial shear strength, the initial shear strength can be obtained by direct shear test; represents the maximum effective crack width; represents the friction coefficient, determined according to the properties and surface roughness of the concrete aggregate; represents the normal stress; represents the actual crack width;

[0107] (2) The elastic coefficient of the bidirectional contact unit is determined according to the biting and synergistic force transmission capacity between cracks at the fracturing position, a plurality of bidirectional contact units are arranged at the crack position of the fractured cement concrete slab, the biting and synergistic force transmission capacity between 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 the thickness is divided into nodes, assuming that the joint width between the plates is zero, the relationship between the elastic coefficient of the bidirectional contact unit and the biting and synergistic force transmission capacity between cracks is as follows:

[0108] ,

[0109] ,

[0110] wherein represents the elastic coefficient of the bidirectional contact unit; represents the shear displacement difference of the corresponding nodes on both sides of the crack at the fracturing position; represents the shear strain between the cracks at the fracturing position;

[0111] The elastic coefficient of the bidirectional contact unit is obtained from the relationship between the elastic coefficient of the bidirectional contact unit and the biting and synergistic force transmission capacity between cracks at the fracturing position, and the calculation formula is as follows:

[0112] ,

[0113] wherein represents the shear modulus of the material, represents the Young's modulus of the material;

[0114] (3) The dynamic deflection meter is used to measure the deflection curve of the slab under load, and the equivalent resilient modulus of the base layer is calculated, and the shear deformation of both sides of the crack at the fracturing position is evaluated according to the elastic coefficient of the bidirectional contact unit and the equivalent resilient modulus of the base layer, and the calculation formula is as follows:

[0115] ,

[0116] ;

[0117] wherein represents the shear deformation of both sides of the crack, represents the load diffusion coefficient of the pavement structure, represents the deformation value at the load center;

[0118] (4) When the asphalt overlay layer with different thickness is paved, the influence of the change of crack synergistic force transmission performance on the shear stress of asphalt overlay layer is calculated by trial, when the crack synergistic force transmission performance is poor, the shear stress at the crack is obviously increased, therefore, the change rule of the shear stress at the bottom of asphalt overlay layer under different force transmission performance of the pressure crack of old cement pavement is analyzed;

[0119] / (1+ );

[0120] wherein, represents the vertical shear stress at the bottom of asphalt overlay layer;

[0121] When the shear type cracking surface at the bottom of asphalt layer is along the vertical direction, the cracking surface and the direction of vertical shear stress are consistent, the vertical shear stress at the bottom of asphalt overlay layer is used to replace the shear stress in the structure;

[0122] (5) Shear deformation index of pressure crack of old cement pavement:

[0123] When the Mohr-Coulomb strength theory is used to check the shear strength, the shear stress in the asphalt overlay structure is limited to not more than the shear strength of the material of the structure layer, that is, , according to the Coulomb theory, the shear strength is calculated, , represents the normal stress on the possible failure surface of the structure layer, and are the cohesion and internal friction angle of the material respectively; The shear stress level and the ultimate shear stress

[0124] of asphalt overlay layer obtained from shear fatigue test, the shear fatigue equation is obtained by linear fitting, the calculation formula is as follows:

[0125] ,

[0126] wherein, represents the fatigue number;

[0127] The allowable shear strength is calculated according to the fatigue number and the ultimate shear stress , ;

[0128] The shear stress in the structure, the shear strength of the material of the structure layer and the allowable shear strength are compared to judge the state of asphalt overlay layer:

[0129] when​​ At this time, the asphalt overlay has an immediate risk of damage;

[0130] When At this time, the asphalt overlay is in a fatigue damage accumulation stage;

[0131] When At this time, the asphalt overlay is in a safe state.

[0132] Example 2

[0133] In order to better prove the technical effect of the present application, according to the finite element numerical calculation results, by setting different elastic coefficients of the two-way contact unit at the joint , a wheel load of 100 KN is applied, the size is 22 cm x 16 cm, the horizontal normal stress, shear stress and crack shear deformation index of the asphalt overlay bottom are measured, according to the Coulomb strength theory, the ultimate shear strength and allowable shear strength of the asphalt overlay bottom surface are calculated, the crack shear deformation index is determined according to the equivalent resilience modulus of the plate bottom foundation and the required fatigue cracking number N, the results under different conditions are shown in Table 1;

[0134] Table 1 Ultimate shear strength and allowable shear strength calculation results of asphalt overlay bottom

[0135]

[0136] The ultimate shear strength and allowable shear strength data of the asphalt overlay bottom are converted into curves, the crack shear deformation index corresponding to the intersection point of the two curves is the crack shear deformation reaching the fatigue life of the allowable shear strength curve, the crack shear deformation index corresponding to N=1000 and N=5000 under different equivalent resilience modulus is shown in Table 2;

[0137] Table 2 Crack shear deformation index

[0138]

[0139] The operation process of estimating the state of the asphalt overlay according to the above results is as follows:

[0140] (1) Determine the parameters: determine the equivalent resilience modulus Et of the plate bottom foundation and the required fatigue cracking number N;

[0141] (2) Look up the table: find the corresponding crack shear deformation standard in the table according to the determined equivalent resilience modulus Et and the required fatigue cracking number N value;

[0142] (3) Linear interpolation: if the values of Et and N are not on the directly given values in the table, linear interpolation is needed to estimate the crack shear deformation;

[0143] (4) Comparison: compare the calculated or tabled crack shear deformation value with the actually measured crack shear deformation value, if the actual crack shear deformation value exceeds the standard value given in the table, then the structure or pavement needs to be reinforced or maintained.

[0144] The crack shear deformation index can be linearly interpolated in the table according to the equivalent resilient modulus of the plate bottom foundation and the required number of fatigue cracking, and the deflection difference in the process of different fatigue cracking loads is below the standard value, which indicates that the state of the asphalt overlay at this time is better; when the shear deformation value is greater than the standard value, the asphalt overlay at this time does not meet the normal use, and needs to be maintained.

[0145] The above describes the specific embodiments of the application in combination with the drawings, but is not a limitation on the protection scope of the application, and various modifications or variations made by those skilled in the art on the basis of the technical solutions of the application without creative labor are still within the protection scope of the application.

Claims

1. A method for estimating the state of an asphalt overlay based on the state of a cement pavement under fracturing, characterized by the steps of As follows: S1, collecting relevant data of cement pavement; S2, using finite element numerical calculation method to construct the old cement concrete pavement fracturing model, specifically using two-way contact element to simulate the engagement state of the old cement concrete pavement fracturing crack, analyzing the influence of two-way contact element elastic coefficient and the support condition of the fracturing cement concrete slab bottom on the shear deformation of the fracturing crack; S3, constructing the composite model of the old cement concrete pavement after fracturing and the asphalt overlay, and obtaining the state of the asphalt overlay by calculating the fatigue life and allowable shear stress of the asphalt overlay on the fracturing crack; According to the composite model of the old cement concrete pavement after fracturing and the asphalt overlay, the state of the asphalt overlay is predicted, and the specific operation is as follows: (1) Calculate the shear force between the cracks, and determine the crack engagement and force transmission capacity according to the shear force between the cracks; The shear force between the cracks is the stress perpendicular to the crack propagation direction acting on the crack surface, and the engagement and force transmission capacity between the cracks is the ability of the concrete aggregate to resist crack propagation through mutual engagement and friction, and the shear force between the cracks is equivalent to the engagement and force transmission capacity between the cracks, and the calculation formula of the shear force between the cracks is as follows: ， wherein, represents the shear force between fractures at the fracture treatment, i.e. the ability of the fractures to bite and transfer load together; represents the initial shear strength; represents the maximum effective fracture width; represents the friction coefficient; represents the normal stress; represents the actual fracture width; (2) The elastic coefficient of the bidirectional contact unit is determined according to the bite synergistic force transmission capacity between cracks, a plurality of bidirectional contact units are arranged at the cracks of the fractured cement concrete slab, the bite synergistic force transmission capacity between cracks is simulated by controlling the elastic coefficient of the bidirectional contact unit, the width of the fractured cement concrete slab is set as , the thickness is set as , the thickness is divided into nodes, the joint width between the slabs is assumed to be zero, and the relationship between the elastic coefficient of the bidirectional contact unit and the bite synergistic force transmission capacity between cracks is as follows: ， ， wherein, represents the elastic coefficient of the bi-directional contact unit; represents the difference of shear displacement of the corresponding nodes on both sides of the fracture at the fracturing site; represents the shear strain between the fractures at the fracturing site; The elastic coefficient of the bidirectional contact unit is obtained from the relationship between the elastic coefficient of the bidirectional contact unit and the occlusion cooperation force transmission capacity between fractures at the fracturing position , and the calculation formula is as follows: ， wherein, G represents the shear modulus of the material, E represents the Young's modulus of the material; (3) The dynamic deflectometer is used to measure the deflection curve under the plate load, and the equivalent resilient modulus of the base layer is calculated The shear deformation on both sides of the fracturing fracture is evaluated according to the elastic coefficient of the two-way contact unit and the equivalent resilient modulus of the base layer, and the calculation formula is as follows: ， ； wherein, represents the shear deformation of both sides of the crack, represents the load dispersion coefficient of the pavement structure, represents the deformation value at the load center; (4) When the asphalt overlay of different thickness is added, the influence of the change of crack cooperative force transmission performance on the shear stress of asphalt overlay is calculated by trial, when the crack cooperative force transmission performance is poor, the shear stress at the crack increases obviously, therefore, the change rule of the bottom shear stress of asphalt overlay under different force transmission performance of old cement pavement fracturing crack is analyzed; / (1+ )； wherein, represents the vertical shear stress at the bottom of the asphalt overlay layer; When the asphalt layer bottom surface shear type cracking surface is along the vertical direction, the cracking surface and the vertical shear stress direction are consistent, and the vertical shear stress at the asphalt overlay layer bottom is used Instead of the internal shear stress of the structure ; (5) Old cement pavement fracturing crack shear deformation index: The shear stress in the asphalt overlay structure is limited when checking the shear strength by Mohr-Coulomb strength theory not exceeding the shear strength of the structural layer material i.e. The shear strength is calculated according to Coulomb theory, , the normal stress on the possible failure surface of the structural layer, and the cohesion and the internal friction angle of the material, respectively Shear stress levels of asphalt overlays from shear fatigue tests and ultimate shear stress The shear fatigue equation was obtained by linear fitting, and the calculation formula is as follows: ， wherein, represents the number of cycles to failure; According to the number of fatigue cycles and the ultimate shear stress Calculating the allowable shear strength , ; Shear stress within the comparative structure Shear strength of the structural layer material And the allowable shear strength To judge the state of the asphalt overlay When the asphalt overlay is at risk of immediate failure; When the asphalt overlay is in the fatigue damage accumulation phase; When the asphalt overlay is in a safe condition.

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

3. The method of claim 2, wherein the method is characterized by: Based on the collected relevant data of cement pavement, the old cement concrete pavement fracturing model is constructed by using finite element numerical calculation method, and the specific operation is as follows: Full constraint boundary conditions are applied to the bottom surface of the old cement concrete pavement fracturing model, so that the displacement of the model in each direction is zero; The free boundary condition is applied to the side surface of the old cement concrete pavement fracturing model, so that the displacement of the side surface node in each direction is not limited; The degree of freedom of the top node of the old cement concrete pavement fracturing model is kept open.

4. The method for estimating the state of the asphalt overlay based on the state of the cement pavement according to claim 3, characterized in that, The operation process of using finite element numerical calculation method to establish the old cement concrete pavement fracturing model is as follows: (1) Establish components or models: according to the actual engineering requirements, create geometric components or overall models, and determine the length, width of the fracturing old cement concrete slab and the foundation depth; (2) Assign material properties: specify the corresponding material properties for each component in the model, including the thickness, elastic modulus, Poisson's ratio and density of the fracturing cement concrete slab; (3) Contact setting: determine the contact type, friction coefficient and constraint relationship of the cement concrete road and asphalt overlay after fracturing; (4) Boundary conditions and loads: Set boundary conditions: set the bottom of the model completely fixed, and set the lateral constraint to apply symmetric boundary conditions; Determine the load: determine the applied load and the shape of the wheel load on the ground; (5) Meshing and post-processing: Determine the mesh type, then meshing; Determine the key results of post-processing; (6) Analyze the shear deformation of the crack at the fracture.

5. The method for estimating the state of the asphalt overlay based on the state of the cement pavement according to claim 4, wherein The engagement state of the crack at the fracture of the old cement concrete pavement is simulated by the bidirectional contact element, and the specific operation is as follows: Set multiple bidirectional contact elements at the fractured crack, adjust the size of the elastic coefficient of the bidirectional contact element according to the actual crack engagement state, and simulate the mechanical behavior under different crack engagement states by controlling the elastic coefficient of the bidirectional contact element; Apply load at the wheel load position, and perform local mesh refinement processing on the load position. Refine the mesh at the crack of the fractured cement concrete slab and the position of the asphalt overlay near the crack.

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

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