Pavement structure design method based on fatigue damage of semi-rigid base asphalt pavement

Abstract

The invention provides a pavement structure design method based on fatigue damage of a semi-rigid base asphalt pavement, and relates to the technical field of road engineering design. According to traffic parameters of the semi-rigid base asphalt pavement within a design age limit, an equivalent damage method is utilized to calculate an accumulated equivalent axis number of a semi-rigid base and an asphalt layer, and an initial design scheme of the semi-rigid base asphalt pavement is determined; calculating accumulated damage and modulus attenuation values of the semi-rigid base layer under the load action by utilizing a semi-rigid base layer modulus attenuation model in analysis periods one by one, acquiring pavement structure response of the semi-rigid base layer asphalt pavement based on an elastic stratified theory, and calculating the fatigue life of the semi-rigid base layer and accumulated fatigue damage of the asphalt layer by utilizing a fatigue estimation model. And updating and adjusting the design scheme of the semi-rigid base asphalt pavement until all analysis periods are traversed, and determining the optimal design scheme of the semi-rigid base asphalt pavement. The influence of modulus attenuation of the semi-rigid base is fully considered, and the long-term durability of the asphalt pavement is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of road engineering design, and in particular to a pavement structure design method based on fatigue damage of a semi-rigid base asphalt pavement. Background Art

[0002] Semi-rigid base asphalt pavement is a widely used asphalt pavement structure. Although it has shortcomings such as serious early damage, its low cost is unmatched by other asphalt pavement structures. As a result, semi-rigid base asphalt pavement structure will remain the main structural form of highway pavement structure for a long time in the future.

[0003] At present, the design method of semi-rigid base asphalt pavement in the current asphalt pavement specifications in my country only verifies the fatigue damage of the semi-rigid base, and the modulus of the semi-rigid base needs to be constant, which is inconsistent with the actual state of the structure. In fact, the modulus of the semi-rigid base material will continue to decay under the combined effects of traffic loads and the environment.

[0004] Therefore, it is urgent to fully consider the influence of the modulus attenuation of semi-rigid base materials on the fatigue damage of asphalt pavement during service, and propose a pavement structure design method based on fatigue damage of semi-rigid base asphalt pavement to guide the pavement structure design of semi-rigid base asphalt pavement. Summary of the invention

[0005] In order to address the deficiencies of the above-mentioned prior art, the present invention proposes a pavement structure design method based on fatigue damage of semi-rigid base asphalt pavement, taking the cumulative fatigue damage of the asphalt layer within the design life as the main indicator, and comprehensively considering the influence of the modulus attenuation of the semi-rigid base during the service of the asphalt pavement, thereby achieving an accurate prediction of the fatigue damage of the asphalt pavement within the design life, providing a basis for formulating the optimal design scheme for the semi-rigid base asphalt pavement, and laying a foundation for ensuring the long-term durability of the asphalt pavement.

[0006] The present invention adopts the following technical solutions:

[0007] The pavement structure design method based on fatigue damage of semi-rigid base asphalt pavement includes the following steps:

[0008] Step 1, obtaining the design life of the semi-rigid base asphalt pavement to be laid, and collecting traffic parameters of the road section where the semi-rigid base asphalt pavement to be laid is located within the design life;

[0009] Step 2, using the equivalent damage method to calculate the equivalent axle load times corresponding to fatigue cracking of the semi-rigid base and the equivalent axle load times corresponding to fatigue cracking of the asphalt layer in the semi-rigid base asphalt pavement, obtain the cumulative equivalent axle load times of the semi-rigid base and the asphalt layer, and determine the initial design scheme of the semi-rigid base asphalt pavement;

[0010] Step 3, dividing the accumulated equivalent axle times of the semi-rigid base and the asphalt layer into multiple analysis periods;

[0011] Step 4: Analyze each period one by one, use the semi-rigid base modulus attenuation model to calculate the cumulative damage and modulus attenuation value of the semi-rigid base under load, combine the asphalt layer modulus and the roadbed modulus, obtain the pavement structure response of the semi-rigid base asphalt pavement based on the elastic layered theory, obtain the bottom bending tensile stress of the semi-rigid base and the asphalt layer, use the fatigue prediction model to calculate the fatigue life of the semi-rigid base and the cumulative fatigue damage of the asphalt layer and compare them with the preset judgment conditions, update and adjust the initial design scheme of the semi-rigid base asphalt pavement, until all analysis periods are traversed, and obtain the material modulus attenuation curve of each structural layer in the semi-rigid base in the semi-rigid base asphalt pavement and the cumulative fatigue damage curve of the asphalt layer;

[0012] Step 5: Output the optimal design scheme for the semi-rigid base asphalt pavement.

[0013] Preferably, the traffic parameters include the annual average daily traffic volume AADTT, the annual traffic volume growth rate γ, the direction coefficient DDF and the lane coefficient LDF.

[0014] Preferably, in the initial design scheme of the asphalt pavement structure, the asphalt pavement structure is provided with a roadbed, a semi-rigid base layer and a surface layer from bottom to top, wherein the roadbed is provided as a soil base with a modulus of 80 MPa and a Poisson's ratio of 0.4; the semi-rigid base layer is provided with a plurality of structural layers, which are provided as an upper base layer, a lower base layer and a subbase layer from top to bottom, wherein the upper base layer and the lower base layer are paved with inorganic binder stabilized materials, the subbase layer is paved with inorganic binder stabilized materials, the thickness of the upper base layer is 180 mm, the modulus is 13000 MPa, the Poisson's ratio is 0.25, and the thickness of the lower base layer is 180 mm , modulus is 13000MPa, Poisson's ratio is 0.25, the thickness of the base layer is 180mm, the modulus is 7000MPa, and the Poisson's ratio is 0.25; the surface layer is an asphalt layer, which is paved with asphalt mixture and has multiple structural layers, which are arranged from top to bottom as an upper layer, a middle layer and a lower layer, among which the thickness of the upper layer is 40mm, the modulus is 11000MPa, and the Poisson's ratio is 0.25, the thickness of the middle layer is 60mm, the modulus is 9000MPa, and the Poisson's ratio is 0.25, and the thickness of the lower layer is 80mm, the modulus is 9000MPa, and the Poisson's ratio is 0.25.

[0015] Preferably, when calculating the number of equivalent axle load actions corresponding to fatigue cracking of the semi-rigid base layer, the semi-rigid base layer equivalent axle load conversion coefficient is set to 12, and when calculating the number of equivalent axle load actions corresponding to fatigue cracking of the asphalt layer, the asphalt layer axle load conversion coefficient is set to 4.

[0016] Preferably, the step 4 includes the following sub-steps:

[0017] Step 4.1, according to the initial design plan of the semi-rigid base asphalt pavement, obtain the initial value of the modulus of each structural layer in the roadbed, semi-rigid base and surface layer;

[0018] Step 4.2, combining the number of loads in the current analysis period, using the semi-rigid base modulus attenuation model to calculate the modulus value of each structural layer of the semi-rigid base after load attenuation, and obtaining the modulus value of each structural layer in the semi-rigid base after load action;

[0019] Step 4.3, according to the modulus values ​​of each structural layer in the semi-rigid base layer, the modulus values ​​of each structural layer in the surface layer and the modulus value of the roadbed in the current analysis period, the pavement structure response of the semi-rigid base asphalt pavement is obtained based on the elastic layered theory system, the bending tensile stress at the bottom of the semi-rigid base layer and the bending tensile stress at the bottom of the asphalt layer are obtained, and are substituted into the fatigue prediction model;

[0020] Step 4.4, using the fatigue prediction model to calculate, obtain the fatigue life of each structural layer in the semi-rigid base and the accumulated fatigue damage of the asphalt layer;

[0021] Step 4.5, comparing the fatigue life of each structural layer in the semi-rigid base with the preset cumulative equivalent axle times, if the fatigue life of a structural layer in the semi-rigid base is greater than the preset cumulative equivalent axle times, then entering the next analysis period, continue to use the semi-rigid base modulus attenuation model to calculate the modulus value of the structural layer in the semi-rigid base after the load effect is attenuated, otherwise, the modulus of the structural layer is set to a fixed value according to the preset semi-rigid base modulus value;

[0022] Step 4.6, comparing the accumulated fatigue damage of the asphalt layer with the preset accumulated fatigue damage threshold of the asphalt layer, if the accumulated fatigue damage of the asphalt layer is not less than the preset accumulated fatigue damage threshold of the asphalt layer, adjusting the thickness and modulus of the asphalt layer, otherwise, retaining the current design of the asphalt layer;

[0023] Step 4.7, according to the thickness and modulus value of each structural layer in the semi-rigid base and asphalt layer in the current analysis period, obtain the optimized semi-rigid base asphalt pavement design scheme, and enter step 4.8;

[0024] Step 4.8, determine whether all analysis periods have been traversed. If not, proceed to step 4.9 to enter the next analysis period. Otherwise, proceed to step 4.10;

[0025] Step 4.9, repeating steps 4.2 to 4.8 to optimize the design scheme of the semi-rigid base asphalt pavement in the current analysis period;

[0026] Step 4.10, end the optimization of the semi-rigid base asphalt pavement design scheme, determine the optimal design scheme of the semi-rigid base asphalt pavement, and obtain the material modulus attenuation curve of each structural layer in the semi-rigid base of the semi-rigid base asphalt pavement and the cumulative fatigue damage curve of the asphalt layer.

[0027] Preferably, the semi-rigid base modulus attenuation model is:

[0028]

[0029] in,

[0030]

[0031] In the formula, E n-CTB is the modulus of the semi-rigid base after the load acts n times, in MPa; E 最小 is the minimum value of the semi-rigid base modulus, in MPa; E 最大 It is the maximum value of the modulus of the semi-rigid base, which is used to indicate the modulus value of the semi-rigid base under the undamaged state, and the unit is MPa; D CTB is the cumulative damage of the semi-rigid base after the load acts n times; i is the analysis period number; k is the total number of analysis periods; n i,j is the number of times the j-th level load acts in the i-th analysis period, in times; N i,j is the fatigue life of the j-th load in the ith analysis period, in times.

[0032] Preferably, the fatigue prediction model includes a semi-rigid base layer fatigue life prediction model and an asphalt layer cumulative fatigue damage prediction model;

[0033] The fatigue life prediction model of the semi-rigid base layer is:

[0034]

[0035] Where N is the fatigue life of the semi-rigid base, in times; σ t is the bending tensile stress at the bottom of the semi-rigid base layer, in MPa; R s K is the flexural strength of the semi-rigid base material, in MPa; c is the on-site adjustment coefficient of fatigue life of semi-rigid base; β is the reliability coefficient of asphalt pavement;

[0036] The cumulative fatigue damage prediction model of the asphalt layer is:

[0037]

[0038] in,

[0039]

[0040] Where D is the accumulated fatigue damage of the asphalt layer; i is the analysis period number; k is the total number of analysis periods; D i is the fatigue damage of the asphalt layer in the i-th analysis period; m i Nf is the number of load actions in the i-th analysis period, in times; 1i is the fatigue life of the asphalt layer in the i-th analysis period, in times; ε i is the tensile strain value applied in the i-th analysis period, in με; S i is the initial flexural modulus of the mixture in the asphalt layer, in MPa; VFA is the asphalt saturation, in %.

[0041] The present invention has the following beneficial effects:

[0042] The present invention proposes a pavement structure design method based on fatigue damage of semi-rigid base asphalt pavement. The method fully considers the influence of semi-rigid base modulus attenuation and cumulative fatigue damage of asphalt layer on asphalt pavement structure, and estimates the cumulative fatigue damage of asphalt layer of pavement structure within the design life by truly restoring the semi-rigid base modulus attenuation process during the actual service of the pavement structure. The asphalt pavement structure design scheme is optimized, which effectively prevents fatigue damage of pavement structure within the design life and is conducive to ensuring the long-term durability of the asphalt pavement. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a flow chart of a pavement structure design method based on fatigue damage of semi-rigid base asphalt pavement.

[0044] Figure 2 Schematic diagram of semi-rigid base asphalt pavement structure.

[0045] Figure 3 It is the material modulus attenuation curve of each structural layer of the semi-rigid base asphalt pavement.

[0046] Figure 4 is the cumulative damage curve of the asphalt layer.

[0047] In the figure: 1, roadbed, 2, subbase, 3, lower base, 4, upper base, 5, lower layer, 6, middle surface layer, 7, upper layer. DETAILED DESCRIPTION

[0048] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0049] In this embodiment, the semi-rigid base asphalt pavement is paved in a certain province and belongs to a highway. According to the investigation and analysis of the traffic start and end points, the starting pile number of the semi-rigid base asphalt pavement is 0 and the ending pile number is 40. The pavement structure design method based on fatigue damage of the semi-rigid base asphalt pavement proposed by the present invention is applied to the pavement structure design of the above-mentioned semi-rigid base asphalt pavement. Figure 1 As shown, the following steps are included:

[0050] Step 1: Obtain the design life of the semi-rigid base asphalt pavement and collect traffic parameters of the road section where the semi-rigid base asphalt pavement is to be laid within the design life.

[0051] In this embodiment, the design life of the semi-rigid base asphalt pavement is 15 years, the average daily traffic volume AADTT of the road section where the semi-rigid base asphalt pavement is located is 12406 vehicles / day, the annual traffic growth rate γ is 2.5%, the directional coefficient DDF is 55.0%, and the lane coefficient LDF is 50.0%.

[0052] Step 2: Use the equivalent damage method to calculate the equivalent axle load times corresponding to fatigue cracking of the semi-rigid base and the equivalent axle load times corresponding to fatigue cracking of the asphalt layer in the semi-rigid base asphalt pavement, obtain the cumulative equivalent axle load times of the semi-rigid base and the asphalt layer, and determine the initial design scheme of the semi-rigid base asphalt pavement.

[0053] In this embodiment, the equivalent damage method in the prior art is used, the equivalent axle load conversion coefficient of the semi-rigid base layer is set to 12, and the axle load conversion coefficient of the asphalt layer is set to 4. It is calculated that the number of equivalent axle load actions corresponding to fatigue cracking of the semi-rigid base layer is 1862700100 times, and the number of equivalent axle load actions corresponding to fatigue cracking of the asphalt layer is 27477800 times.

[0054] The initial design scheme of the asphalt pavement structure is shown in Table 1.

[0055] Table 1 Initial design scheme of asphalt pavement structure

[0056] Structural layer number Structure layer name Material Type Thickness(mm) Modulus (MPa) Poisson's ratio 1 Upper layer Asphalt mixture 40 11000 0.25 2 Middle layer Asphalt mixture 60 9000 0.25 3 The lower layer Asphalt mixture 80 9000 0.25 4 Go to the grassroots Inorganic binder stabilized materials 180 13000 0.25 5 Go to the grassroots Inorganic binder stabilized materials 180 13000 0.25 6 Subbase Inorganic binder stabilized materials 180 7000 0.25 7 Roadbed Soil foundation - 80 0.4

[0057] As shown in Table 1, the semi-rigid base asphalt pavement structure in this embodiment is provided with a roadbed 1, a semi-rigid base and a surface layer from bottom to top. Figure 2As shown, the roadbed 1 is set as a soil base with a modulus of 80 MPa and a Poisson's ratio of 0.4; the semi-rigid base is provided with multiple structural layers, which are arranged from top to bottom as an upper base 4, a lower base 3 and a subbase 2, wherein the upper base 4 and the lower base 3 are paved with inorganic binder stabilized materials, and the subbase 2 is paved with inorganic binder stabilized materials. The thickness of the upper base 4 is 180 mm, the modulus is 13000 MPa, and the Poisson's ratio is 0.25, the thickness of the lower base 3 is 180 mm, the modulus is 13000 MPa, and the Poisson's ratio is 0.25, and the thickness of the subbase 2 is 180 mm, modulus of 7000MPa, and Poisson's ratio of 0.25; the surface layer is an asphalt layer, which is paved with asphalt mixture and has multiple structural layers, which are arranged from top to bottom as an upper layer 7, a middle layer 6 and a lower layer 5, wherein the upper layer 7 is an SMA-13 ​​layer with a thickness of 40mm, a modulus of 11000MPa, and a Poisson's ratio of 0.25; the middle layer 6 is an AC-20 layer with a thickness of 60mm, a modulus of 9000MPa, and a Poisson's ratio of 0.25; and the lower layer 5 is an AC-25 layer with a thickness of 80mm, a modulus of 9000MPa, and a Poisson's ratio of 0.25.

[0058] Step 3: Divide the cumulative equivalent axle times of the semi-rigid base and the asphalt layer into 120 analysis periods at equal intervals.

[0059] Step 4: Calculate the cumulative damage and modulus attenuation value of the semi-rigid base under load using the semi-rigid base modulus attenuation model for each analysis period. Combine the asphalt layer modulus and the roadbed modulus to obtain the pavement structure response of the semi-rigid base asphalt pavement based on the elastic layered theory, obtain the bottom bending tensile stress of the semi-rigid base and the asphalt layer, calculate the fatigue life of the semi-rigid base and the fatigue damage accumulation of the asphalt layer using the fatigue prediction model and compare them with the preset judgment conditions, and update and adjust the initial design scheme of the semi-rigid base asphalt pavement until all analysis periods are traversed to obtain the material modulus attenuation curve of each structural layer in the semi-rigid base in the semi-rigid base asphalt pavement and the cumulative damage curve of the asphalt layer. Specifically, the following sub-steps are included:

[0060] Step 4.1, according to the initial design plan of the semi-rigid base asphalt pavement, obtain the initial value of the modulus of each structural layer in the roadbed, semi-rigid base and surface layer.

[0061] Step 4.2, combined with the number of loads in the current analysis period, the modulus value after load attenuation is calculated for each structural layer of the semi-rigid base using the semi-rigid base modulus attenuation model, and the modulus value of each structural layer in the semi-rigid base after load action is obtained.

[0062] The semi-rigid base modulus attenuation model is:

[0063]

[0064] in,

[0065]

[0066] In the formula, E n-CTB E is the modulus of the semi-rigid base after the load acts n times, in MPa; 最小 is the minimum value of the semi-rigid base modulus, in MPa; E 最大 It is the maximum value of the modulus of the semi-rigid base, which is used to indicate the modulus value of the semi-rigid base under the undamaged state, and the unit is MPa; D CTB is the cumulative damage of the semi-rigid base after the load acts n times; i is the analysis period number; k is the total number of analysis periods; n i,j is the number of times the j-th level load acts in the i-th analysis period, in times; N i,j is the fatigue life of the j-th load in the ith analysis period, in times.

[0067] Step 4.3, according to the modulus values ​​of each structural layer in the semi-rigid base layer, the modulus values ​​of each structural layer in the surface layer and the modulus value of the roadbed in the current analysis period, the pavement structure response of the semi-rigid base asphalt pavement is obtained based on the elastic layered theoretical system, the bottom bending tensile stress of the semi-rigid base layer and the bottom bending tensile stress of the asphalt layer are obtained, and substituted into the fatigue prediction model, the fatigue prediction model includes the semi-rigid base fatigue life prediction model and the asphalt layer cumulative fatigue damage prediction model.

[0068] Step 4.4, using the fatigue life prediction model of the semi-rigid base layer in the fatigue prediction model to calculate the fatigue life of each structural layer in the semi-rigid base layer, and then using the cumulative fatigue damage prediction model of the asphalt layer in the fatigue prediction model to calculate the cumulative fatigue damage of the asphalt layer.

[0069] The fatigue life prediction model of the semi-rigid base layer is:

[0070]

[0071] Where N is the fatigue life of the semi-rigid base, in times; σ t is the bending tensile stress at the bottom of the semi-rigid base layer, in MPa; R s K is the flexural strength of the semi-rigid base material, in MPa; c is the on-site adjustment coefficient of fatigue life of semi-rigid base; β is the reliability coefficient of asphalt pavement.

[0072] In the semi-rigid base fatigue life prediction model, the semi-rigid base fatigue life field adjustment coefficient K c It is determined according to the thickness of the inorganic binder layer above the calculation point, as shown in Table 2.

[0073] Table 2 Table of values ​​for on-site adjustment coefficients of fatigue life of semi-rigid base

[0074]

[0075] The asphalt pavement reliability coefficient β is determined according to the highway grade, as shown in Table 3.

[0076] Table 3 Asphalt pavement reliability coefficient value table

[0077] Highway Class highway First-class highway Secondary roads Third-level highway Class IV highway Target reliability (%) 95 90 85 80 70 Reliability coefficient 1.65 1.28 1.04 0.84 0.52

[0078] In this embodiment, the on-site adjustment coefficient K of the fatigue life of the semi-rigid base layer c The value is 0.65, and the reliability coefficient β of asphalt pavement is 1.65.

[0079] The cumulative fatigue damage prediction model of the asphalt layer is:

[0080]

[0081] in,

[0082]

[0083] Where D is the accumulated fatigue damage of the asphalt layer; i is the analysis period number; k is the total number of analysis periods; D i is the fatigue damage of the asphalt layer in the i-th analysis period; m i Nf is the number of load actions in the i-th analysis period, in times; 1i is the fatigue life of the asphalt layer in the i-th analysis period, in times; ε i is the tensile strain value applied in the i-th analysis period, in με; S i is the initial flexural modulus of the mixture in the asphalt layer, in MPa; VFA is the asphalt saturation, in %.

[0084] Step 4.5, compare the fatigue life of each structural layer in the semi-rigid base with the preset cumulative equivalent axial times. If the fatigue life of a structural layer in the semi-rigid base is greater than the preset cumulative equivalent axial times Ne, adjust the thickness of the corresponding structural layer; otherwise, set the modulus of the corresponding structural layer to a fixed value of 2000 MPa according to the preset semi-rigid base modulus value.

[0085] Step 4.6, compare the cumulative fatigue damage of the asphalt layer with the preset cumulative fatigue damage threshold of 0.1. If the cumulative fatigue damage D of the asphalt layer is not less than 0.1, adjust the thickness and modulus of the asphalt layer; otherwise, retain the current design of the asphalt layer.

[0086] Step 4.7, according to the thickness and modulus value of each structural layer in the semi-rigid base and the thickness and modulus value of each structural layer in the asphalt layer in the current analysis period, obtain the optimized semi-rigid base asphalt pavement design plan and enter step 4.8.

[0087] Step 4.8, determine whether all analysis periods have been traversed. If not, proceed to step 4.9 to enter the next analysis period. Otherwise, proceed to step 4.10.

[0088] Step 4.9, repeat steps 4.2 to 4.8 to optimize the design scheme of the semi-rigid base asphalt pavement in the current analysis period.

[0089] Step 4.10, stop optimizing the design scheme of the semi-rigid base asphalt pavement, end the calculation of the accumulated fatigue damage of the asphalt layer, and determine the optimal design scheme of the semi-rigid base asphalt pavement.

[0090] Figure 3 The material modulus attenuation curve of each structural layer of the semi-rigid base asphalt pavement is analyzed. Figure 3 The modulus attenuation of the semi-rigid base layer is known, and when the design life is reached, the modulus of the base layer has decayed to 2000MPa. Figure 4 is the cumulative damage curve of the asphalt layer, and the Figure 4 It can be obtained that when the semi-rigid base asphalt pavement with the optimal design scheme reaches the design life, the cumulative fatigue damage of the asphalt layer is 0.021, which is less than the preset cumulative fatigue damage threshold of 0.1 for the asphalt layer, and meets the preset fatigue damage design requirements for the semi-rigid base asphalt pavement.

[0091] In summary, the method of the present invention comprehensively considers the influence of the modulus attenuation of the semi-rigid base layer on the fatigue damage of the asphalt pavement during the service life of the asphalt pavement, realizes the accurate prediction of the fatigue damage of the asphalt pavement within the design life, provides a basis for guiding the formulation of the optimal design scheme for the semi-rigid base asphalt pavement, and is beneficial to preventing fatigue damage from occurring during the service life of the asphalt pavement.

[0092] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A pavement structure design method based on fatigue damage of semi-rigid base asphalt pavement, characterized in that: The following steps are involved: Step 1, obtaining the design life of the semi-rigid base asphalt pavement to be laid, and collecting traffic parameters of the road section where the semi-rigid base asphalt pavement to be laid is located within the design life; Step 2, using the equivalent damage method to calculate the equivalent axle load times corresponding to fatigue cracking of the semi-rigid base and the equivalent axle load times corresponding to fatigue cracking of the asphalt layer in the semi-rigid base asphalt pavement, obtain the cumulative equivalent axle load times of the semi-rigid base and the asphalt layer, and determine the initial design scheme of the semi-rigid base asphalt pavement; Step 3, dividing the accumulated equivalent axle times of the semi-rigid base and the asphalt layer into multiple analysis periods; Step 4: Analyze each period one by one, use the semi-rigid base modulus attenuation model to calculate the cumulative damage and modulus attenuation value of the semi-rigid base under load, combine the asphalt layer modulus and the roadbed modulus, obtain the pavement structure response of the semi-rigid base asphalt pavement based on the elastic layered theory, obtain the bottom bending tensile stress of the semi-rigid base and the asphalt layer, use the fatigue prediction model to calculate the fatigue life of the semi-rigid base and the cumulative fatigue damage of the asphalt layer and compare them with the preset judgment conditions, update and adjust the initial design scheme of the semi-rigid base asphalt pavement, until all analysis periods are traversed, and obtain the material modulus attenuation curve of each structural layer in the semi-rigid base in the semi-rigid base asphalt pavement and the cumulative fatigue damage curve of the asphalt layer; Step 5: Output the optimal design scheme for the semi-rigid base asphalt pavement.

2. The pavement structure design method based on fatigue damage of semi-rigid base asphalt pavement according to claim 1 is characterized in that: The traffic parameters include the annual average daily traffic volume AADTT, the annual traffic volume growth rate γ, the direction coefficient DDF and the lane coefficient LDF.

3. The pavement structure design method based on fatigue damage of semi-rigid base asphalt pavement according to claim 1 is characterized in that: In the initial design scheme of the asphalt pavement structure, the asphalt pavement structure is provided with a roadbed, a semi-rigid base layer and a surface layer from bottom to top, wherein the roadbed is provided with a soil base with a modulus of 80MPa and a Poisson's ratio of 0.4; the semi-rigid base layer is provided with a plurality of structural layers, which are provided with an upper base layer, a lower base layer and a subbase layer from top to bottom, wherein the upper base layer and the lower base layer are paved with inorganic binder stabilized materials, and the subbase layer is paved with inorganic binder stabilized materials, the thickness of the upper base layer is 180mm, the modulus is 13000MPa, and the Poisson's ratio is 0.25, the thickness of the lower base layer is 180mm, the modulus is 13000MPa, and the Poisson's ratio is 0.25 The modulus is 13000MPa and the Poisson's ratio is 0.25; the thickness of the base layer is 180mm, the modulus is 7000MPa and the Poisson's ratio is 0.25; the surface layer is an asphalt layer, which is paved with asphalt mixture and has multiple structural layers, which are arranged from top to bottom as an upper layer, a middle layer and a lower layer, wherein the thickness of the upper layer is 40mm, the modulus is 11000MPa and the Poisson's ratio is 0.25, the thickness of the middle layer is 60mm, the modulus is 9000MPa and the Poisson's ratio is 0.25, and the thickness of the lower layer is 80mm, the modulus is 9000MPa and the Poisson's ratio is 0.

25.

4. The pavement structure design method based on fatigue damage of semi-rigid base asphalt pavement according to claim 1 is characterized in that: When calculating the number of equivalent axle load actions corresponding to fatigue cracking of the semi-rigid base, the semi-rigid base equivalent axle load conversion factor used is set to 12. When calculating the number of equivalent axle load actions corresponding to fatigue cracking of the asphalt layer, the asphalt layer axle load conversion factor used is set to 4.

5. The pavement structure design method based on fatigue damage of semi-rigid base asphalt pavement according to claim 1 is characterized in that: The step 4 includes the following sub-steps: Step 4.1, according to the initial design plan of the semi-rigid base asphalt pavement, obtain the initial value of the modulus of each structural layer in the roadbed, semi-rigid base and surface layer; Step 4.2, combining the number of loads in the current analysis period, using the semi-rigid base modulus attenuation model to calculate the modulus value of each structural layer of the semi-rigid base after load attenuation, and obtaining the modulus value of each structural layer in the semi-rigid base after load action; Step 4.3, according to the modulus values ​​of each structural layer in the semi-rigid base layer, the modulus values ​​of each structural layer in the surface layer and the modulus value of the roadbed in the current analysis period, the pavement structure response of the semi-rigid base asphalt pavement is obtained based on the elastic layered theory system, the bending tensile stress at the bottom of the semi-rigid base layer and the bending tensile stress at the bottom of the asphalt layer are obtained, and are substituted into the fatigue prediction model; Step 4.4, using the fatigue prediction model to calculate, obtain the fatigue life of each structural layer in the semi-rigid base and the accumulated fatigue damage of the asphalt layer; Step 4.5, comparing the fatigue life of each structural layer in the semi-rigid base with the preset cumulative equivalent axle times, if the fatigue life of a structural layer in the semi-rigid base is greater than the preset cumulative equivalent axle times, then entering the next analysis period, continue to use the semi-rigid base modulus attenuation model to calculate the modulus value of the structural layer in the semi-rigid base after the load effect is attenuated, otherwise, the modulus of the structural layer is set to a fixed value according to the preset semi-rigid base modulus value; Step 4.6, comparing the accumulated fatigue damage of the asphalt layer with the preset accumulated fatigue damage threshold of the asphalt layer, if the accumulated fatigue damage of the asphalt layer is not less than the preset accumulated fatigue damage threshold of the asphalt layer, adjusting the thickness and modulus of the asphalt layer, otherwise, retaining the current design of the asphalt layer; Step 4.7, according to the thickness and modulus value of each structural layer in the semi-rigid base and asphalt layer in the current analysis period, obtain the optimized semi-rigid base asphalt pavement design scheme, and enter step 4.8; Step 4.8, determine whether all analysis periods have been traversed. If not, proceed to step 4.9 to enter the next analysis period. Otherwise, proceed to step 4.10; Step 4.9, repeating steps 4.2 to 4.8 to optimize the design scheme of the semi-rigid base asphalt pavement in the current analysis period; Step 4.10, end the optimization of the semi-rigid base asphalt pavement design scheme, determine the optimal design scheme of the semi-rigid base asphalt pavement, and obtain the material modulus attenuation curve of each structural layer in the semi-rigid base of the semi-rigid base asphalt pavement and the cumulative fatigue damage curve of the asphalt layer.

6. The pavement structure design method based on fatigue damage of semi-rigid base asphalt pavement according to claim 5 is characterized in that: The semi-rigid base modulus attenuation model is: in, In the formula, E n-CTB is the modulus of the semi-rigid base after the load acts n times, in MPa; E 最小 is the minimum value of the semi-rigid base modulus, in MPa; E 最大 is the maximum value of the modulus of the semi-rigid base, which is used to indicate the modulus value of the semi-rigid base under the undamaged state, in MPa; DCTB is the cumulative damage of the semi-rigid base after the load acts n times; i is the analysis period number; k is the total number of analysis periods; n i,j is the number of times the j-th level load acts in the i-th analysis period, in times; N i,j is the fatigue life of the j-th load in the ith analysis period, in times.

7. The pavement structure design method based on fatigue damage of semi-rigid base asphalt pavement according to claim 5 is characterized in that: The fatigue prediction model includes a semi-rigid base fatigue life prediction model and an asphalt layer cumulative fatigue damage prediction model; The fatigue life prediction model of the semi-rigid base layer is: Where N is the fatigue life of the semi-rigid base, in times; σ t is the bending tensile stress at the bottom of the semi-rigid base layer, in MPa; R s K is the flexural strength of the semi-rigid base material, in MPa; c is the on-site adjustment coefficient of fatigue life of semi-rigid base; β is the reliability coefficient of asphalt pavement; The cumulative fatigue damage prediction model of the asphalt layer is: in, Where D is the accumulated fatigue damage of the asphalt layer; i is the analysis period number; k is the total number of analysis periods; D i is the fatigue damage of the asphalt layer in the i-th analysis period; m i Nf is the number of load actions in the i-th analysis period, in times; 1i is the fatigue life of the asphalt layer in the i-th analysis period, in times; ε i is the tensile strain value applied in the i-th analysis period, in με; S i is the initial flexural modulus of the mixture in the asphalt layer, in MPa; VFA is the asphalt saturation, in %.

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