Method for evaluating the state of the overall-layer-interlayer structure of asphalt pavement road

Abstract

The application discloses a kind of asphalt pavement road whole-layer-interlayer structure state evaluation method, belong to road structure bearing capacity evaluation index field.The method includes: with nondestructive testing technique, the measured modulus value of each layer position is obtained, the various evaluation indexes of road whole-layer-interlayer structure state are constructed, and the structure state of each layer position is realized " five points system " evaluation by calculation method.The asphalt pavement road whole-layer-interlayer structure state evaluation method proposed in the application unifies the mechanical response quantity selected by structure evaluation index and design index, constructs the road structure state evaluation index based on new design index, and conforms to the integration concept of road structure design and evaluation.

Description

Technical Field

[0001] This invention relates to an evaluation index for the bearing capacity of road structures, and more particularly to a method for evaluating the overall-layer-interlayer structural state of asphalt pavement. Background Technology

[0002] Based on current engineering practice and theoretical analysis, the existing methods for evaluating the state of road structures mainly have the following problems:

[0003] Problem 1: The evaluation indicators are too simplistic. The current evaluation standards only use a single PSSI indicator. This indicator only reflects the overall structural bearing capacity of the road structure layers and cannot reflect the layered structural state and interlayer bonding state of the surface layer, base layer, and subgrade. For the same PSSI value, the corresponding surface layer, base layer, subgrade, and interlayer structural states can vary greatly. Furthermore, for road sections with poor PSSI values, the weakest layer cannot be determined using the PSSI indicator.

[0004] Problem 2: Insufficient Applicability of Deflection Standard Values. Both the early SSI index and the current PSSI index evaluate road structural condition based on pavement deflection. The standard deflection values ​​compared to measured deflection within these indices lack applicability. With the improvement of socio-economic levels, asphalt mixtures have become the primary material for asphalt pavements. Furthermore, the thickness and strength of asphalt pavements and water-stabilized base courses have significantly improved compared to nearly 30 years ago. Numerous studies have pointed out that the formulaic pavement design deflection calculation method has insufficient applicability in the current context. In the 2017 version of the current design specifications, the conversion method for equivalent axle load application times has undergone significant changes compared to the 2006 and 1997 versions. The calculation method based on the old axle load conversion method is no longer compatible with the current axle load conversion method.

[0005] Question 3: Inconsistency between the mechanical response quantities selected for structural evaluation and design indices. The 2017 version of the current design code no longer uses deflection as a design index. For semi-rigid base asphalt pavements, the permanent deformation of the asphalt layer and the tensile stress at the bottom of the semi-rigid base layer corresponding to fatigue cracking life are used as design indices. Although the 2018 version of the current evaluation standard changed the pavement design deflection value in the calculation formula to a standard pavement deflection value, this value is no longer a design index, and it is no longer calculated for newly built or reconstructed roads. This results in a disconnect between road structure design and evaluation indices. Constructing a road structure state evaluation index based on the new design indices aligns with the integrated concept of road structure design and evaluation. Summary of the Invention

[0006] This invention addresses the four problems and shortcomings of existing road structure evaluation indicators and methods by providing an evaluation index for the overall-layer-interlayer structural state of semi-rigid base asphalt pavements based on non-destructive testing technology. This method utilizes the results obtained from on-site non-destructive testing on highways to characterize the interlayer state of the road, showing a strong positive correlation with actual service conditions, thus providing a precise basis for assessing road performance degradation and subsequent maintenance decisions.

[0007] The present invention adopts the following technical solution:

[0008] The results obtained from non-destructive testing techniques at highway sites characterize the interlayer condition of highways and show a strong positive correlation with actual service conditions. This provides a precise basis for assessing the later performance degradation of roads and making subsequent maintenance decisions, including the following steps:

[0009] Step (1), Layer and interlayer structural parameter detection: Use various non-destructive testing methods to obtain the modulus E of the asphalt surface layer and the modulus E of the semi-rigid water-stabilized base layer. B Roadbed modulus E G The friction coefficient f between the surface layer and the base layer; where the measured modulus of the asphalt surface layer should be corrected to the modulus at 20℃;

[0010] Step (2), Mechanical response calculation: Construct an elastic layered finite element model of the road design state and an actual state finite element model;

[0011] The average value ε of the maximum vertical compressive strain at the top of the asphalt surface layer under the road design condition was calculated using both the finite element model of the road design condition and the finite element model of the actual condition. ro The average value ε of the maximum vertical compressive strain at the top of each layer in the asphalt pavement under actual structural conditions. r ;

[0012] The maximum tensile strain ε at the bottom of the semi-rigid base layer under the road design state was calculated using both the finite element model of the road design state and the finite element model of the actual state. o The maximum tensile strain ε at the bottom of the semi-rigid base layer under actual structural conditions;

[0013] The maximum deflection l of the roadbed top surface under the road design state was calculated using both the finite element model of the road design state and the finite element model of the actual state. so The maximum deflection l of the top surface of the roadbed under actual structural conditions s .

[0014] Step (3), Calculation of layered structure state coefficients: Based on the mechanical response calculation in step (2), the average value of each maximum vertical compressive strain under the road design state and the actual structural state, the maximum tensile strain at the bottom of the semi-rigid base layer, and the maximum deflection of the top surface of the subgrade are obtained.

[0015] The surface / base / subgrade structure condition ratio (SCR), base structure condition ratio (BCR), and roadbed structure condition ratio (GCR) are calculated using the following formulas.

[0016]

[0017] Step (4), Calculation of overall-layer-interlayer structural state index: Based on step (3), the surface layer structural state coefficient SCR, base layer structural state coefficient BCR, and subgrade structural state coefficient GCR are calculated;

[0018] The surface layer structure state index SSCI, base layer structure state index BSCI, and subgrade structure state index GSCI are calculated using the following formulas.

[0019]

[0020] In the above formula: E E0 For the design modulus of semi-rigid water-stabilized base course, E G0 For the design modulus of the roadbed;

[0021] Based on the friction coefficient between the surface layer and the base layer obtained in step (1), the interlayer structural condition index ISCI (Surface / Base / Subgrade Structure Condition Index) is calculated; the road structure condition index RSCI (Road Structure Condition Index) is calculated by weighting the layer and interlayer structural condition indices.

[0022] Step (5): Based on the surface layer structure state index SSCI, base layer structure state index BSCI, subgrade structure state index GSCI, interlayer structure state index ISCI, or road structure state index RSCI.

[0023] The overall, layered, and interlayer structural conditions of the road are evaluated according to the table below.

[0024]

[0025] Step (6): Based on the overall-layer-interlayer structural state index calculated in step (4) and the graded evaluation table in step (5), when any of the road structure state index RSCI, surface layer structure state index SSCI, base layer structure state index BSCI, or subgrade structure state index GSCI is evaluated as inferior or poor, repair measures should be taken for the asphalt pavement as a whole.

[0026] The method for evaluating the overall-layer-interlayer structural state of asphalt pavement described in this invention incorporates a breaker mechanism when calculating the road structure state index RSCI in step (4). The breaker mechanism is as follows: if there are longitudinal cracks in the evaluated road section caused by uneven settlement of the subgrade, regardless of whether they extend to the road surface, the RSCI value of this road section is evaluated as 0 points.

[0027] The method for evaluating the overall-layer-interlayer structural state of asphalt pavement described in this invention uses the asphalt surface layer modulus E and the semi-rigid water-stabilized base layer modulus E obtained in step (1) in step (2). B Roadbed modulus E G The friction coefficient f between the surface layer and the base layer is used for the structure of the finite element model of the component in actual state; the mechanical response of the road is calculated based on the action of a double-circle uniformly distributed load.

[0028] The method for evaluating the overall-layer-interlayer structural state of asphalt pavement according to the present invention, in step (6),

[0029] When the Road Structure Condition Index (RSCI) is rated as medium, it is recommended to take overall repair measures for the asphalt pavement.

[0030] When the Road Structure Condition Index (RSCI) is rated as good, repair measures can be taken for the asphalt pavement as a whole.

[0031] When the Road Structure Condition Index (RSCI) is rated as excellent, the asphalt pavement is in good service condition and requires no repair.

[0032] The method for evaluating the overall-layer-interlayer structural state of asphalt pavement according to the present invention, in step (6),

[0033] When any of the following indices is rated as medium in the surface layer structure condition index (SSCI), base layer structure condition index (BSCI), or subgrade structure condition index (GSCI), it is recommended to take necessary repair measures for that layer and above.

[0034] When a certain index among the surface layer structure condition index (SSCI), base layer structure condition index (BSCI), or subgrade structure condition index (GSCI) is rated as good, necessary repair measures can be taken for that layer and above.

[0035] When the surface layer structure condition index (SSCI), base layer structure condition index (BSCI), or subgrade structure condition index (GSCI) are all excellent, the service condition of each layer of the asphalt pavement is healthy and requires no repair.

[0036] The method for evaluating the overall-layer-interlayer structural state of asphalt pavement according to the present invention, in step (6),

[0037] When the Interlayer Structure State Index (ISCI) is rated as medium or below, it is recommended to take overall repair measures for the asphalt pavement.

[0038] When the Interlayer Structure Condition Index (ISCI) is rated as good or above, the interlayer condition is excellent and no repair is required.

[0039] The method for evaluating the overall-layered-interlayer structural state of asphalt pavement according to the present invention includes the following steps in step (2) of constructing an elastic layered finite element model of the road design state:

[0040] Step (2-1): Query the initial road design data to obtain the thickness, Poisson's ratio, modulus, density, and interlayer friction coefficient of the three layers of the road design state: the lower layer, the base layer, and the subgrade. Construct a road design state model accordingly.

[0041] Step (2-2): Detect the actual structural state of the road and obtain the thickness, Poisson's ratio, modulus, density, and interlayer friction coefficient of the three layers of the road: the lower layer, the base layer, and the subgrade. Construct an actual structural state model based on this information.

[0042] Steps (2-3): Apply symmetric boundary conditions to the corresponding sides of the constructed road design state model and actual structural state model, and simplify the model calculation by constructing a quarter-symmetric finite element model;

[0043] The upper surface of the road design state model and the actual structural state model is an unconstrained surface. Except for the upper surface and the side surface with symmetrical boundary conditions, the displacement in all directions of the other side surface and the bottom surface is set to 0.

[0044] The mesh is generated using eight-node hexahedral elements. To balance simulation accuracy and efficiency, the mesh is densest in the region directly below the load, followed by the surface layer and base layer, while the subgrade mesh is sparsest.

[0045] The surface layer is divided into 4-6 layers with even smaller thicknesses;

[0046] Step (2-4): Construct the road design state model and actual structural state model according to (2-1) to (2-3) and calculate: The line connecting the two centers of the double circular load coincides with the axis of symmetry of the model surface, and the midpoint of the line coincides with the geometric center of the surface.

[0047] Apply loads and begin calculations to simulate the maximum mechanical response at the load center, one radius from the center, 1.5 radius from the center, and two radius from the center at the junction of the surface layer, base layer, and subgrade. This includes the average value ε of the maximum vertical compressive strain at the top of each layer in the surface layer under road design conditions. ro The maximum tensile strain ε at the bottom of the semi-rigid base layer o Maximum deflection of the top surface of the subgrade l so;

[0048] The average value ε of the maximum vertical compressive strain at the top of the layers in the actual structural state. r The maximum tensile strain ε at the bottom of the semi-rigid base layer, and the maximum deflection l at the top surface of the subgrade. s .

[0049] By employing the above technical solutions, the present invention has the following beneficial effects compared to the prior art:

[0050] 1. The asphalt pavement overall-layer-interlayer structural state evaluation method proposed in this invention has good comprehensiveness. It can not only reflect the overall structural bearing capacity of the road structure layers, but also reflect the layered structural state and interlayer bonding state of the surface layer, base layer and subgrade.

[0051] 2. The evaluation method for the overall-layer-interlayer structural state of asphalt pavement proposed in this invention has good applicability. It fully considers the evolution of the main materials of the asphalt surface layer, the thickness and strength of the asphalt surface layer and the water-temperature base layer, and constructs an evaluation method that is more suitable for current engineering practice.

[0052] 3. The asphalt pavement overall-layer-interlayer structural state evaluation method proposed in this invention unifies the mechanical response quantities selected by the structural evaluation index and the design index, and constructs a road structure state evaluation index based on the new design index, which is in line with the concept of integrated road structure design and evaluation. Attached Figure Description

[0053] Figure 1 A road model under double circular loads.

[0054] (a) is a top view diagram;

[0055] (b) is a quarter-symmetric finite element model;

[0056] (c) represents the four measurement points for various mechanical response quantities in surface A of the model. Detailed Implementation

[0057] To make the objectives and technical solutions of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0058] Evaluation method for the overall-layer-interlayer structural condition of asphalt pavement: The steps are as follows:

[0059] (1) Layer and interlayer structural parameter detection: E is obtained by applying various non-destructive testing methods. B =1600GP0,E G =220GP0, ε r =-34, ε=-43, l s =280 (1 / 100 mm), f = 0.8 (modulus corrected to 20℃).

[0060] (2) Mechanical Response Calculation: A finite element model of the road under both design and actual conditions was constructed, with the structural parameters of the actual condition model using the results obtained in (1). The mechanical response at various points along the road under a uniformly distributed double-circle load was calculated. The load settings and calculation locations for each mechanical response quantity are detailed in the following section. Figure 1 As shown.

[0061] Step (2) Constructing the finite element model of the road design state in an elastic layered manner includes the following sub-steps:

[0062] (2.1) The road finite element model consists of three layers: an 18cm asphalt mixture surface layer, a 40cm water-stabilized crushed stone base layer, and a 542cm subgrade. In the finite element model, each structural layer is set as an elastic homogeneous medium. The Coulomb friction model is used between the surface layer and the base layer to characterize their bonding state with the friction coefficient. The base layer and the subgrade are set as completely continuous.

[0063] (2.2) Different combinations of layered and interlayer structural state parameters were set in the constructed finite element model, as shown in Appendix Table 2, resulting in a total of 256 road models with different structural state combinations.

[0064] (2.3) Symmetrical boundary conditions were applied to the corresponding sides of the constructed road finite element model to simplify the model calculation, thus constructing a quarter-symmetric finite element model. The upper surface of the road model is an unconstrained surface. Except for the upper surface and the sides with symmetric boundary conditions, the displacements in all directions of the other sides and the bottom surface are set to 0. Eight-node hexahedral elements are used to divide the mesh. To balance simulation accuracy and efficiency, the mesh is densest in the region directly below the load, followed by the asphalt surface layer and the cement-stabilized crushed stone base course, while the subgrade mesh is sparsest.

[0065] (2.4) In the simulation, the 18cm thick asphalt surface layer is divided into six layers from top to bottom: 2cm, 2cm, 2cm, 2cm, 2cm, and 8cm thick.

[0066] (2.5) The mechanical response quantities simulated by the finite element road model include the following six items: the average compressive stress and average compressive strain at the top of each asphalt layer, the tensile stress and tensile strain at the bottom of the water-stabilized base layer, the deflection at the top of the subgrade, and the deflection of the road surface. The road model and corresponding dimensional settings under double circular loads are shown in [reference needed]. Figure 1As shown in the figure, for the various mechanical response quantities of the road under load, the simulation yields the maximum mechanical response quantities at points I, II, III, and IV in Figure 1.

[0067] (3) Calculation of Layered Structure Condition Ratio: Based on the calculation results of the mechanical response in (2), the surface layer structure condition ratio (SCR), base layer structure condition ratio (BCR), and subgrade structure condition ratio (GCR) are calculated according to equation (1). Where ε ro and ε r These are the average values ​​of the maximum vertical compressive strain at the top of each layer of the asphalt pavement under road design and actual structural conditions. The layering method of the asphalt pavement is based on the 2017 edition of the current design specifications; ε o ε and ε represent the maximum tensile strain at the bottom of the semi-rigid base layer under the road design and actual structural conditions, respectively; l so and l s ε represents the maximum deflection of the top surface of the roadbed under road design and actual structural conditions, where ε is the maximum deflection of the roadbed top surface. r0 =-30, ε0=-40,

[0068]

[0069] The results were: SCR = 0.93, BCR = 0.93, GCR = 0.89

[0070] (4) Calculation of the overall-layer-interlayer structural condition index: Using formula (2), based on the SCR, BCR, and GCR values ​​obtained in (3), calculate the surface layer structural condition index SSCI, base layer structural condition index BSCI, and subgrade structural condition index GSCI; based on the friction coefficient between the surface layer and base layer obtained in (1), calculate the interlayer structural condition index ISCI (Surface / Base / Subgrade Structure Condition Index); calculate the road structure condition index RSCI (Road Structure Condition Index) by averaging the layered and interlayer structural condition indices. There is a breaker mechanism in the calculation of RSCI. If there are longitudinal cracks caused by uneven settlement of the subgrade in the evaluated road section, regardless of whether they extend to the road surface, the RSCI value of this road section is directly rated as 0.

[0071]

[0072] The results were: SSGI = 90.24, BSCI = 88.79, GSCI = 89.03, ISCI = 90.02

[0073] (5) Based on the surface layer structure state index SSCI, base layer structure state index BSCI, subgrade structure state index GSCI, interlayer structure state index ISCI or road structure state index RSCI, the overall-layer-interlayer structure state of the road is evaluated according to Table 1.

[0074] Evaluation results: Surface layer condition rating "Excellent"; base course structure condition rating "Good"; subgrade structure condition rating "Good"; interlayer structure condition rating "Excellent"; pavement structure strength condition rating "Good".

[0075] (6) Based on the evaluation results, the repair recommendations given in this standard are: necessary repair measures can be taken for the asphalt pavement as a whole.

[0076] Table 1. Grading Evaluation Method for Overall-Layer-Interlayer Structural Status of Roads

[0077]

[0078] Table 2 Road Structure Status Grades in the 1996 Edition of the Evaluation Standard

[0079]

[0080] Table 3. Road Structure Status Grades in the 2007 and 2018 Current Evaluation Standards

[0081]

[0082] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for evaluating the overall, layered, and interlayer structural condition of asphalt pavement, characterized by: Includes the following steps: Step (1), Layer and interlayer structural parameter detection: Use non-destructive testing methods to obtain the modulus E of the asphalt surface layer and the modulus E of the semi-rigid water-stabilized base layer. B Roadbed modulus E G The friction coefficient f between the surface layer and the base layer; Step (2), Mechanical response calculation: Construct an elastic layered finite element model of the road design state and an actual state finite element model; The average value ε of the maximum vertical compressive strain at the top of the asphalt surface layer under the road design condition was calculated using both the finite element model of the road design condition and the finite element model of the actual condition. ro The average value ε of the maximum vertical compressive strain at the top of each layer in the asphalt pavement under actual structural conditions. r ; The maximum tensile strain ε at the bottom of the semi-rigid base layer under the road design state was calculated using both the finite element model of the road design state and the finite element model of the actual state. o The maximum tensile strain ε at the bottom of the semi-rigid base layer under actual structural conditions; The maximum deflection l of the roadbed top surface under the road design state was calculated using both the finite element model of the road design state and the finite element model of the actual state. so The maximum deflection l of the top surface of the roadbed under actual structural conditions s ; Step (3), Calculation of layered structure state coefficients: Based on the mechanical response calculation in step (2), the average value of each maximum vertical compressive strain under the road design state and the actual structural state, the maximum tensile strain at the bottom of the semi-rigid base layer, and the maximum deflection of the top surface of the subgrade are obtained. The surface layer structure state coefficient (SCR), base layer structure state coefficient (BCR), and subgrade structure state coefficient (GCR) are calculated using the following formulas. Step (4), Calculation of overall-layer-interlayer structural state index: Based on step (3), the surface layer structural state coefficient SCR, base layer structural state coefficient BCR, and subgrade structural state coefficient GCR are calculated; The surface layer structure state index SSCI, base layer structure state index BSCI, and subgrade structure state index GSCI are calculated using the following formulas. In the above formula: E B0 For the design modulus of semi-rigid water-stabilized base course, E G0 For the design modulus of the roadbed; Based on the friction coefficient between the surface layer and the base layer obtained in step (1), the interlayer structural state index ISCI is calculated; the road structural state index RSCI is calculated by weighting the layer and interlayer structural state indices. Step (5): Based on the surface layer structure state index SSCI, base layer structure state index BSCI, subgrade structure state index GSCI, interlayer structure state index ISCI, or road structure state index RSCI. The overall, layered, and interlayer structural conditions of the road are evaluated according to the table below. Step (6): Based on the overall-layer-interlayer structural state index calculated in step (4) and the graded evaluation table in step (5), when any of the road structure state index RSCI, surface layer structure state index SSCI, base layer structure state index BSCI, or subgrade structure state index GSCI is evaluated as inferior or poor, repair measures should be taken for the asphalt pavement as a whole.

2. The method for evaluating the overall-layer-interlayer structural state of asphalt pavement according to claim 1, characterized in that: In step (4), a circuit breaker mechanism is added when calculating the Road Structure State Index (RSCI). The circuit breaker mechanism is as follows: if there are longitudinal cracks in the evaluated road section caused by uneven settlement of the roadbed, the RSCI value of this road section is evaluated as 0 points.

3. The method for evaluating the overall-layer-interlayer structural state of asphalt pavement according to claim 1, characterized in that: In step (2), the modulus E of the asphalt surface layer and the modulus E of the semi-rigid water-stabilized base layer obtained in step (1) are used. B Roadbed modulus E G The friction coefficient f between the surface layer and the base layer is used for the structure of the finite element model of the component in actual state; the mechanical response of the road is calculated based on the action of a double-circle uniformly distributed load.

4. The method for evaluating the overall-layer-interlayer structural state of asphalt pavement according to claim 1, characterized in that: In step (6), When the Road Structure Condition Index (RSCI) is rated as medium, it is recommended to take overall repair measures for the asphalt pavement. When the Road Structure Condition Index (RSCI) is rated as good, repair measures can be taken for the asphalt pavement as a whole. When the Road Structure Condition Index (RSCI) is rated as excellent, the asphalt pavement is in good service condition and requires no repair.

5. The method for evaluating the overall-layer-interlayer structural state of asphalt pavement according to claim 1, characterized in that: In step (6), When any of the following indices is rated as medium in the surface layer structure condition index (SSCI), base layer structure condition index (BSCI), or subgrade structure condition index (GSCI), it is recommended to take necessary repair measures for that layer and above. When a certain index among the surface layer structure condition index (SSCI), base layer structure condition index (BSCI), or subgrade structure condition index (GSCI) is rated as good, necessary repair measures can be taken for that layer and above. When the surface layer structure condition index (SSCI), base layer structure condition index (BSCI), or subgrade structure condition index (GSCI) are all excellent, the service condition of each layer of the asphalt pavement is healthy and requires no repair.

6. The method for evaluating the overall-layer-interlayer structural state of asphalt pavement according to claim 1, characterized in that: In step (6), When the Interlayer Structure State Index (ISCI) is rated as medium or below, it is recommended to take overall repair measures for the asphalt pavement. When the Interlayer Structure Condition Index (ISCI) is rated as good or above, the interlayer condition is excellent and no repair is required.

7. The method for evaluating the overall-layer-interlayer structural state of asphalt pavement according to claim 1, characterized in that: Step (2) of constructing the elastic layered road design state finite element model includes the following steps: Step (2-1): Query the initial road design data to obtain the thickness, Poisson's ratio, modulus, density, and interlayer friction coefficient of the three layers of the road design state: the lower layer, the base layer, and the subgrade. Construct a road design state model accordingly. Step (2-2): Detect the actual structural state of the road and obtain the thickness, Poisson's ratio, modulus, density, and interlayer friction coefficient of the three layers of the road: the lower layer, the base layer, and the subgrade. Construct an actual structural state model based on this information. Steps (2-3): Apply symmetric boundary conditions to the corresponding sides of the constructed road design state model and actual structural state model, and simplify the model calculation by constructing a quarter-symmetric finite element model; The upper surface of the road design state model and the actual structural state model is an unconstrained surface. Except for the upper surface and the side surface with symmetrical boundary conditions, the displacement in all directions of the other side surface and the bottom surface is set to 0. The grid is divided using eight-node hexahedral elements. The grid is densest in the area directly below the load, followed by the surface layer and base layer, while the grid of the subgrade is sparsest. The surface layer is divided into 4-6 layers with even smaller thicknesses; Step (2-4): Construct the road design state model and actual structural state model according to (2-1) to (2-3) and calculate: The line connecting the two centers of the double circular load coincides with the axis of symmetry of the model surface, and the midpoint of the line coincides with the geometric center of the surface. Apply loads and begin calculations to simulate the maximum mechanical response at the load center, one radius from the center, 1.5 radius from the center, and two radius from the center at the junction of the surface layer, base layer, and subgrade. This includes the average value ε of the maximum vertical compressive strain at the top of each layer in the surface layer under road design conditions. ro The maximum tensile strain ε at the bottom of the semi-rigid base layer o Maximum deflection of the top surface of the subgrade l so ; The average value ε of the maximum vertical compressive strain at the top of the layers in the actual structural state. r The maximum tensile strain ε at the bottom of the semi-rigid base layer, and the maximum deflection l at the top surface of the subgrade. s .

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