A method for determining the cumulative standard axle load action times of asphalt pavement based on rut depth

Abstract

The present invention belongs to the field of road asphalt pavement structure design, and particularly relates to a method for determining the cumulative standard axle load action times of asphalt pavement based on rut depth. This method uses the rut depth of existing asphalt pavement as the basic parameter and calculates the equivalent cumulative standard axle load action times for maintenance design based on the following formula: The present invention utilizes the rut depth data of existing asphalt pavement to accurately obtain the cumulative standard axle load action times borne by the existing asphalt pavement after completion and operation. Furthermore, based on this, the cumulative standard axle load action times for design during the maintenance design period can be estimated. This method can avoid traffic volume observation and axle load spectrum investigation, providing a new method with higher accuracy and lower cost for determining the equivalent axle load action times of rut for semi-rigid base asphalt pavement maintenance design.

Description

Technical Field

[0001] The present invention belongs to the field of road asphalt pavement structure design, and particularly relates to a method for determining the cumulative standard axle load application times of an asphalt pavement based on rut depth. Background Art

[0002] As time goes by, different types of diseases occur on the asphalt pavement, and the corresponding pavement performance will gradually decay, resulting in maintenance. In the current road maintenance design, the traffic load survey data of the existing asphalt pavement is a key parameter for guiding the maintenance design. Its functions include determining the traffic load level and calculating the cumulative standard axle load application times corresponding to different pavement damages in the future. Furthermore, according to the cumulative standard axle load application times during the maintenance design period, the maintenance structure form of the asphalt pavement is determined.

[0003] Currently, the "Code for Design of Highway Asphalt Pavements" (JTG D50-2017) (hereinafter referred to as the "Code") has targeted descriptions for traffic volume data surveys. Data collection is carried out in combination with traffic observation stations, and specific requirements include traffic volume, type, lane coefficient, direction coefficient, etc. At the same time, for the maintenance design of asphalt pavements, the "Code for Maintenance Design of Highway Asphalt Pavements" (JTG 5421-2018) stipulates that traffic load surveys are required in the maintenance design, such as "traffic volume and traffic composition data should include at least the traffic volume observation data of the recent 3 years. Axle load spectrum data should be continuously detected using special axle load survey equipment", etc.

[0004] However, the above regulations lack feasibility in many cases. For example, in terms of traffic observation, except for high-grade highways such as expressways, for some low-grade highways, there is a lack of traffic volume observation data. In addition, the cost of special axle load survey equipment is relatively high and the popularity rate is relatively low. In fact, for the maintenance design of a large number of road asphalt pavement structures, only short-term observations of the number of vehicles on the existing pavement are carried out. On the one hand, the obtained traffic volume data is not accurate, and on the other hand, it is difficult to accurately consider the influence of different vehicle loads. Eventually, the accurate cumulative standard axle load application times that the existing pavement will bear after maintenance cannot be obtained, thus affecting the rationality of the maintenance design scheme. In fact, when repeated loads act on the pavement structure, a large amount of permanent deformation (i.e., rut disease) will occur in the structure. In the pavement structure design, rut-related factors are basic and important design contents to be considered. If the existing rut depth of the pavement can be effectively utilized and used as a basic parameter to calculate the axle load times, it can save manpower, time, and economic costs to a certain extent, and the results are also more reliable.

[0005] Therefore, it is necessary to develop a method that does not require traffic volume observation and axle load spectrum survey, and can obtain the cumulative standard axle load application times based on the existing diseases of the asphalt pavement, making the maintenance design results more reliable and targeted.

[0006] At present, regarding the calculation methods related to the cumulative equivalent axle load applications, many scholars in China have conducted extensive research and applied them in various aspects. For example, the "Calculation Method for Cumulative Equivalent Axle Load Applications of Asphalt Pavement on Medium-Capacity Bus Lanes" with the publication number CN112685814A, the "Heavy-Duty Traffic Data Judgment and Classification System for National and Provincial Trunk Highways" with the publication number CN113128834A, the "Prediction Method for the Occurrence Time of Instability-Type Rutting on Asphalt Pavements" with the publication number CN107966548B, the "Rapid Prediction Method for Permanent Deformation of Asphalt Pavements Based on Temperature Distribution in the Full Temperature Range" with the publication number CNl07190622A, the "Axle Load Conversion Method Based on Shear Fatigue Equivalent Failure of Asphalt Layers" with the publication number CN111209667A, etc. The above patents either propose improved calculations for the cumulative axle load applications under specific conditions, prediction methods for the occurrence time of rutting diseases, and system research and development, or require prior investigations on the traffic volume, vehicle types, and axle load composition of the analysis section. Some cannot effectively utilize the existing pavement diseases (rutting diseases), or cannot meet the calculation of cumulative applications under general highway or multiple traffic load conditions. Moreover, the technical means or implementation conditions required by the above patents are relatively complex, and the economic and time costs are relatively high.

[0007] In addition, among numerous maintenance projects, the maintenance projects targeting rutting diseases account for a large proportion in the maintenance projects, and the cumulative axle load times are very important influencing factors, and the current investigation means are costly. Therefore, for the rutting disease maintenance projects, it is necessary to propose a method for determining the cumulative axle load times that can reduce the technical difficulty, save time and economic costs. Summary of the Invention

[0008] In view of the above deficiencies, the present invention provides a method for determining the cumulative standard axle load applications of asphalt pavements based on rut depth. By using the rut depth data of existing asphalt pavements, the cumulative standard axle load applications endured by the existing asphalt pavements after completion and operation can be accurately obtained, providing a reliable basis for maintenance design. At the same time, it is not necessary to conduct cumulative traffic volume observations and axle load spectrum investigations, and the time cost and economic cost are relatively low.

[0009] The present invention is specifically realized through the following technical solutions:

[0010] A method for determining the cumulative standard axle load applications of asphalt pavements based on rut depth, which takes the rut depth of existing asphalt pavements as the basic parameter and through the formula

[0011]

[0012]

[0013]

[0014] Wherein, [R a is the permanent deformation of the asphalt mixture layer (mm); N e5 is the cumulative number of equivalent single-axle loads applied to the design lane in the investigation year (times); T d is the design air temperature (°C); ψ s is the pavement structure coefficient; R τs is the comprehensive penetration strength of each asphalt mixture layer (MPa); t1 is the number of years since the section was opened to traffic (years); N e is the cumulative number of standard axle loads applied during the design period of the maintenance design section (times); t2 is the design life of the section maintenance design (years); N t1 is the cumulative number of equivalent single-axle loads applied to the design lane at the initial year of maintenance design (times); γ is the annual growth rate of traffic volume. By the cumulative number of standard axle loads that the existing asphalt pavement has withstood after completion and operation, the cumulative number of standard axle loads applied during the maintenance design period is obtained. The specific steps are as follows:

[0015] S1. Collection of basic information and rut depth;

[0016] The basic information includes the location of the section, highway grade, road age, pavement type and structural form; according to the rut conditions of different degrees of the existing pavement, collect the low, medium and high point data of the rut depth at the place where the rut changes evenly. The high, medium and low points of the rut are determined according to the rut depth in sequence, and the permanent deformations [R a1 , [R a2 and [R a3 of the three points of the existing semi-rigid base asphalt pavement are determined respectively;

[0017] S2. Determine the structural layer thickness

[0018] At the shoulder position of the same pile number corresponding to the place where the rut occurs evenly, drill multiple asphalt mixture layer and base core samples, and measure the thickness of each structural layer of the core samples, including the thickness h a (mm) of the asphalt mixture surface layer and the thickness h b (mm) of the inorganic binder stabilized base;

[0019] S3. Prepare test specimens

[0020] Before the test, cut the core samples according to the layer position, and complete the preparation of the specimens layer by layer in sequence;

[0021] S4. Determine the comprehensive penetration strength R τs (MPa) of the asphalt mixture layer according to Appendix F, "Test Method for Uniaxial Penetration Strength of Asphalt Mixture" in "Code for Design of Highway Asphalt Pavements" (JTG D50-2017);

[0022] S5. Determine the elastic modulus E of the semi-rigid base material according to the "Test Method for Uniaxial Compressive Modulus of Inorganic Binder Stabilized Materials" in Appendix E of the "Code for Design of Highway Asphalt Pavements" (JTG D50-2017). b (MPa);

[0023] S6. Based on the region where the surveyed section is located, take the average value of the monthly average temperatures greater than 0 °C in the surveyed year in this region as the design temperature T d (°C);

[0024] S7. Calculate the number of times the cumulative standard axle load has acted on the surveyed section

[0025] Calculate and obtain the comprehensive penetration strength R of each asphalt mixture layer τs , pavement structure coefficient ψ s , weight ω of the i-th layer of asphalt mixture is , and calculate and obtain the number of times N of the cumulative standard axle load that the semi-rigid base asphalt pavement has withstood within the surveyed year e5 . The calculation formula is shown in Formulas (1) to (5);

[0026]

[0027]

[0028]

[0029]

[0030]

[0031] In the formula, [R a is the permanent deformation of the asphalt mixture layer (mm); T d is the design temperature (°C); ψ s is the pavement structure coefficient; h a is the thickness of the asphalt mixture layer (mm); h b is the thickness of the inorganic binder stabilized layer (mm); E b is the modulus of the inorganic binder stabilized layer (MPa); R τs is the comprehensive penetration strength of each asphalt mixture layer (MPa); R τi is the penetration strength of the i-th layer of asphalt mixture (MPa); n is the number of layers of asphalt mixture; ω is is the weight of the i-th layer of asphalt mixture, which is the ratio of the shear stress at the midpoint of the thickness of the i-th layer to the sum of the shear stresses at the midpoints of the thicknesses of each layer; N e5 is the number of cumulative equivalent design axle load actions on the design lane in the surveyed year (times);

[0032] N obtained from rut positions at high, medium and low levels e5 , and the average value is taken as the number of cumulative standard axle load applications actually borne by the actual road section;

[0033] S8. Cumulative number of equivalent design axle load applications on the design lane at the initial year of road section opening to traffic

[0034] According to the number of years of road opening to traffic and in combination with the "Code for Design of Highway Asphalt Pavements" (JTG D50 - 2017), calculate the cumulative number of equivalent design axle load applications N1 on the design lane at the initial year of road section opening to traffic. The calculation formula is as shown in Equation (6);

[0035]

[0036] In the formula, N e5 is the cumulative number of equivalent design axle load applications (times) on the design lane in the survey year; t1 is the number of years of road opening to traffic of the road section (years); N1 is the cumulative number of equivalent design axle load applications (times) on the design lane at the initial year of road section opening to traffic; γ is the annual growth rate of traffic volume;

[0037] S9. Calculation of the cumulative number of standard axle load applications during the design period of the maintenance design road section

[0038] Based on the cumulative number of equivalent design axle load applications N1 on the design lane at the initial year of road section opening to traffic and the number of years of road opening to traffic of the road section, obtain the cumulative number of equivalent design axle load applications N t1 at the initial year of maintenance design, and further obtain the cumulative number of standard axle load applications N e during the design period of the maintenance design road section. The calculation formula is as shown in Equation (7);

[0039]

[0040] In the formula, N e is the cumulative number of standard axle load applications (times) during the design period of the maintenance design road section; t2 is the design life (years) of the road section maintenance design; N t1 is the cumulative number of equivalent design axle load applications (times) at the initial year of maintenance design; γ is the annual growth rate of traffic volume;

[0041] S10. Checking and calculating the newly built pavement structure.

[0042] In the "Code", it is required that when designing the semi - rigid base asphalt pavement structure, the penetration strength of the asphalt mixture must meet the strength allowable value according to different highway grades and structural combinations, etc. The cumulative number of equivalent design axle load applications for rutting (i.e., Ne) is one of the important factors affecting the penetration strength of the asphalt mixture. The calculation method of the present invention uses the axle load times obtained from the existing asphalt pavement diseases to back - calculate the design axle load times, which provides a more real and accurate cumulative number of standard axle load applications for maintenance design and makes the pavement structure design more reasonable.

[0043] In the above solution, a calculation method for the equivalent cumulative axle load repetitions of a pavement for maintenance design is proposed. By using the rut depth data of the existing asphalt pavement, the cumulative standard axle load repetitions endured by the existing asphalt pavement after completion and operation can be accurately obtained, eliminating the need for traffic volume observation and axle load spectrum investigation. This provides a new method with higher accuracy and lower cost for calculating the equivalent axle load repetitions of a semi-rigid base asphalt pavement for maintenance design. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a flowchart of a method for determining the cumulative standard axle load repetitions of an asphalt pavement based on rut depth according to an embodiment of the present invention;

[0045] Figure 2 It is a newly built pavement structure diagram drawn up according to an embodiment of the present invention;

[0046] In the figure: 1 - 5 cm SBS modified asphalt mixture; 2 - 7 cm high modulus asphalt mixture AC - 25C; 3 - 60 cm 4.5% cement stabilized base. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] In order to make the objectives and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0048] As Figure 1 shown, an embodiment of the present invention provides a method for determining the cumulative standard axle load repetitions of an asphalt pavement based on rut depth, including the following steps:

[0049] S1. Collection of basic information and rut depth

[0050] The basic information includes the location of the designed section, highway grade, road age, pavement type, and structural form, etc.; according to the rut conditions of different degrees (light, medium, and heavy) of the existing pavement, data of the low, medium, and high points of the rut depth are collected at the locations where the rut changes evenly. The high, medium, and low points of the rut are determined by sorting the rut depth in sequence. According to the rut positions at the high, medium, and low points, the corresponding N e5 , of the three points are obtained, and the average value of the corresponding Ne5 of the three points is taken as the cumulative standard axle load repetitions actually endured by the actual section. Determine the permanent deformation amount [R a of the existing semi-rigid base asphalt pavement;

[0051] S2. Determine the structural layer thickness

[0052] At the shoulder position of the same pile number corresponding to the location where the rut occurs evenly, multiple asphalt mixture layer and base core samples are drilled, and the thickness of each structural layer of the core samples is measured, including the thickness h of the asphalt mixture surface layera (mm) and inorganic binder stabilized base course h b (mm);

[0053] S3. Preparation of test specimens

[0054] Before conducting in - laboratory tests on core samples, it is necessary to cut the core samples using a double - sided saw cutting device. Cut the core samples according to the layer position. The thickness of the specimen depends on the material layer position, and the specimen preparation is completed layer by layer in sequence;

[0055] S4. Determination of the comprehensive penetration strength R of the asphalt mixture layer τs . For the shear strength index, it is carried out according to "Test Method for Uniaxial Penetration Strength of Asphalt Mixture" in Appendix F of the "Code". This method can use core samples drilled on - site for testing.

[0056] S5. Determination of the modulus E of the base core sample b .

[0057] Determine the elastic modulus E of the semi - rigid base material according to "Test Method for Uniaxial Compression Modulus of Inorganic Binder Stabilized Materials" in Appendix E of the "Code" b .

[0058] S6. Determination of the design air temperature T d .

[0059] Based on the area where the surveyed section is located, take the average value of the monthly average air temperatures greater than 0 °C in each month within the surveyed year in this area as the design air temperature T d o

[0060] S7. Calculation of the cumulative standard axle load applications endured by the surveyed section.

[0061] The calculation formula is shown in formulas (1) - (4).

[0062]

[0063]

[0064]

[0065]

[0066] In the formula, [R a is the permanent deformation of the asphalt mixture layer (mm); N e5 is the cumulative number of equivalent design axle load applications on the design lane within the surveyed year (times); T d is the design air temperature (°C); Ψ s is the pavement structure coefficient; h a is the thickness of the asphalt mixture layer (mm); h bis the thickness (mm) of the inorganic binder stabilized layer; E b is the modulus (MPa) of the inorganic binder stabilized layer; R τs is the comprehensive penetration strength (MPa) of each asphalt mixture layer; R τi is the penetration strength (MPa) of the i-th layer of asphalt mixture; n is the number of asphalt mixture layers; ω is is the weight of the i-th layer of asphalt mixture, which is the ratio of the shear stress at the midpoint of the thickness of the i-th layer to the sum of the shear stresses at the midpoints of the thicknesses of each layer. When n = 1, ω1 = 1.0; when n = 2, from top to bottom, ω1 = 0.48; ω2 = 0.52; when n = 3, from top to bottom, ω1 = 0.35, ω2 = 0.42, ω3 = 0.23. The cumulative number of standard axle load applications N endured by the semi-rigid base asphalt pavement within the surveyed year e5 The calculation method is shown in Equation (5).

[0067]

[0068] S8. The cumulative number of equivalent design axle load applications on the design lane at the initial year of road section opening to traffic

[0069] According to the designed service life of the maintenance plan and in combination with the "Code", calculate the cumulative number of equivalent design axle load applications N1 on the design lane at the initial year of road section opening to traffic. The calculation formula is shown in Equation (6);

[0070]

[0071] In the formula, N e5 is the cumulative number of equivalent design axle load applications on the design lane in the surveyed year (times); t1 is the number of years since the road section was opened to traffic (years); N1 is the cumulative number of equivalent design axle load applications on the design lane at the initial year of road section opening to traffic (times); γ is the annual growth rate of traffic volume;

[0072] S9. Calculation of the cumulative number of standard axle load applications during the design period of the maintenance design road section

[0073] Based on the cumulative number of equivalent design axle load applications N1 on the design lane at the initial year of road section opening to traffic and the number of years since the road section was opened to traffic, calculate the cumulative number of equivalent design axle load applications N at the initial year of maintenance design t1 , and further obtain the cumulative number of standard axle load applications N e during the design period of the maintenance design road section. The formula is shown in Equation (7);

[0074]

[0075] In the formula, N e is the cumulative number of standard axle load applications during the design period of the maintenance design road section (times); t2 is the designed service life (years) of the road section maintenance design; N t1is the cumulative number of equivalent single-axle loads (ESALs) on the design lane in the initial year of maintenance design (times); γ is the annual growth rate of traffic volume;

[0076] S10. Checking the newly built pavement structure.

[0077] In the "Code", it is required that when designing the semi-rigid base asphalt pavement structure, the penetration strength of the asphalt mixture must meet the strength allowable value according to different highway grades and structural combinations, etc. The cumulative number of equivalent single-axle loads (i.e., Ne) for rutting is one of the important factors affecting the penetration strength of the asphalt mixture. The calculation method of the present invention back-calculates the design axle load times by using the axle load times obtained from the existing asphalt pavement diseases, which provides a more real and accurate cumulative standard axle load action times for maintenance design and makes the pavement structure design more reasonable.

[0078] Embodiment

[0079] S1. Collecting basic information and rut depth information of the driving lane of the existing road asphalt pavement.

[0080] Taking the Heida Line in Shenyang City, Liaoning Province as an example, the Heida Line (from the Fourth Ring Road to the Liaoyang boundary section) is located in the Sujiatun District of Shenyang City, a secondary highway with two-way 2 lanes and a semi-rigid base asphalt pavement. In 2017, this section of the road was overhauled and opened to traffic. By the time of the road section investigation, it had been open to traffic for 4 years. The pavement structure form after renovation is: 5 cm SBS fine-grained modified asphalt mixture (AC-16C) + 7 cm medium-grained high-modulus modified asphalt mixture (AC-25C) + 60 cm 4.5% cement stabilized macadam base. According to the foregoing method, the permanent deformation amounts of this road section are 7.4 mm, 7.6 mm, and 7.8 mm respectively, that is, [R a1 = 7.4 mm, [R a2 = 7.6 mm, and [R a3 = 7.8 mm.

[0081] S2. Determining the structural layer thickness.

[0082] At the shoulder position corresponding to the same pile number where the rut occurs evenly, drill multiple asphalt mixture layer and base core samples, and measure the thickness of each structural layer of the core samples, including the surface layer thickness and the base layer thickness. After measurement, the surface layer thickness h a = 120 mm, and the base layer thickness h b = 600 mm..

[0083] S3. Preparing test specimens.

[0084] Before conducting the indoor test on the core samples, use a double-sided saw cutting device to cut the shoulder core samples. The height of the surface layer specimen is 50 mm, the height of the lower surface layer specimen is 70 mm, and the height of the base layer specimen is 600 mm.

[0085] S4. Measure the shear strength R of the asphalt mixture τs .

[0086] The shear strength measured by the "Uniaxial Penetration Strength Test Method for Asphalt Mixtures" in Appendix F of the "Specification". The surface layer is two layers of modified asphalt mixture, so the number of layers n = 2. From top to bottom, ω 1s = 0.48, ω 2s = 0.52, R τ1 = 0.808 MPa, R τ2 = 0.690 MPa. Therefore, the comprehensive penetration strength R of the asphalt mixture layer τs = 0.747 MPa.

[0087] The calculation process is as follows.

[0088]

[0089] S5. Measure the modulus E of the base core sample b .

[0090] Determine the elastic modulus E of the semi-rigid base material according to the "Uniaxial Compression Modulus Test Method for Inorganic Binder Stabilized Materials" in Appendix E of the "Specification" b = 20000 MPa.

[0091] S6. Determine the design air temperature T d .

[0092] According to the fact that the surveyed section is located in Shenyang City, Liaoning Province, the average value of the monthly average air temperatures greater than 0 °C in the surveyed year in this area is 14.9 °C. Therefore, the design air temperature T d = 14.9 °C.

[0093] S7. Calculate the number of cumulative standard axle load applications on the surveyed section.

[0094] The calculation process is as follows.

[0095]

[0096]

[0097]

[0098]

[0099]

[0100] S8. The cumulative number of equivalent design axle load applications on the design lane in the initial year of road section opening to traffic.

[0101] According to the number of years since the road was opened to traffic (4 years) and in combination with the "Code", calculate the cumulative number of equivalent design axle loads N1 on the design lane at the initial year of the road section's opening to traffic. The calculation process is as follows.

[0102]

[0103] S9. Calculation of the cumulative number of standard axle loads acting during the design period of the maintenance design road section

[0104] Based on the cumulative number of equivalent design axle loads N1 on the design lane at the initial year of the road section's opening to traffic and the number of years since the road section was opened to traffic (4 years), obtain the cumulative number of equivalent design axle loads N on the design lane at the initial year of the maintenance design. t1 , and further obtain the cumulative number of standard axle loads N acting during the design period of the maintenance design road section e . The calculation process is as follows.

[0105]

[0106] S10. Pavement structure check.

[0107] The proposed pavement structure form after maintenance is as Figure 1 shown, and the relevant parameters are shown in Table 1. Carry out the penetration strength check of the asphalt mixture according to the "Code".

[0108] Table 1 Pavement structure form and parameters after maintenance

[0109]

[0110]

[0111] Therefore, it is required that the comprehensive penetration strength of the asphalt mixture layer in the pavement design should meet this requirement. According to the "Test Method for Uniaxial Penetration Strength of Asphalt Mixture" in Appendix F of the "Code", conduct tests. The penetration strength of the asphalt mixture on the surface layer of the newly proposed pavement structure is measured to be 0.82 MPa, and the penetration strength of the asphalt mixture on the lower layer is 0.88 MPa. Therefore, the comprehensive penetration strength R of the asphalt mixture layer τs is 0.85 MPa, meeting the requirements. Therefore, the penetration strength check of the asphalt mixture passes.

[0112] The above is only the preferred implementation mode of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for determining the cumulative standard axle load application times of an asphalt pavement based on rut depth, characterized in that, This method takes the rut depth of the existing asphalt pavement as the basic parameter, and obtains the cumulative standard axle load application times during the maintenance design period through the cumulative standard axle load application times that the existing asphalt pavement has endured after completion and operation. The calculation formula is as follows: In the formula, [R a is the permanent deformation of the asphalt mixture layer (mm); N e5 is the cumulative number of equivalent single axle loads applied to the design lane during the survey year (times); T d is the design air temperature (°C); ψ s is the pavement structure coefficient; R τs is the comprehensive penetration strength of each asphalt mixture layer (MPa); t1 is the number of years since the section was opened to traffic (years); N e is the cumulative number of standard axle loads applied during the design period of the maintenance design section (times); $t_2$ is the design life (years) of the road section maintenance design; $N$ t1 is the cumulative number of equivalent single-axle loads acting on the design lane in the initial year of the maintenance design (times); $\gamma$ is the annual growth rate of traffic volume.

2. The method for determining the cumulative standard axle load application times of an asphalt pavement according to claim 1, characterized in that, Specifically, it includes the following steps: S1. Collection of basic information and rut depth; The basic information includes the location of the road section, highway grade, road age, pavement type, and structural form; according to the rutting conditions of the existing pavement to varying degrees, data on the low, medium, and high points of the rut depth are collected at the locations where the rutting changes evenly. The high, medium, and low points of the rut are determined by sorting according to the rut depth in sequence, and the permanent deformation amounts of the three points of the existing semi-rigid base asphalt pavement are determined as [R a1 , [R a2 , and [R a3 ; S2. Determination of the structural layer thickness At the shoulder position of the same pile number corresponding to the place where rutting occurs evenly, drill multiple asphalt mixture layer and base course core samples, and measure the thickness of each structural layer of the core samples, including the thickness h a (mm) of the asphalt mixture surface layer and h b (mm) of the inorganic binder stabilized base course; S3. Preparation of test specimens Before the test, the core samples are cut according to the layer position, and the specimen preparation is completed layer by layer in sequence; S4. Determine the comprehensive penetration strength R (MPa) of the asphalt mixture layer according to the "Test Method for Uniaxial Penetration Strength of Asphalt Mixture" in Appendix F of "Code for Design of Highway Asphalt Pavements" "JTG D50-2017". τs (MPa); S5. Determine the elastic modulus E of semi-rigid base course materials in accordance with the "Test Method for Uniaxial Compressive Modulus of Inorganic Binder Stabilized Materials" in Appendix E of "Code for Design of Highway Asphalt Pavements" "JTG D50-2017". b (MPa); S6. Based on the region where the surveyed section is located, use the average value of the monthly average temperatures greater than 0 °C in each month within the surveyed year in this region as the design temperature T d (°C); S7. Calculation of the cumulative standard axle load application times endured by the investigated section Calculate and obtain the comprehensive penetration strength R of each asphalt mixture layer τs , pavement structure coefficient ψ s , the weight ω of the i-th layer of asphalt mixture is , and calculate and obtain the cumulative number of standard axle load applications N that the semi-rigid base asphalt pavement has endured within the surveyed year e5 , and the calculation formulas are as shown in Formulas (1) to (5); Where, [R a is the permanent deformation of the asphalt mixture layer (mm); T d is the design air temperature (°C); ψ s is the pavement structure coefficient; h a is the thickness of the asphalt mixture layer (mm); h b is the thickness of the inorganic binder stabilized layer (mm); E b is the modulus of the inorganic binder stabilized layer (MPa); R τs is the comprehensive penetration strength of each asphalt mixture layer (MPa); R τi is the penetration strength of the i-th layer of asphalt mixture (MPa); n is the number of layers of asphalt mixture; ω is is the weight of the i-th layer of asphalt mixture, which is the ratio of the shear stress at the midpoint of the i-th layer thickness to the sum of the shear stresses at the midpoints of the thicknesses of each layer; N e5 is the cumulative number of equivalent single axle load applications on the design lane in the investigation year (times); N obtained based on rut positions at high, medium, and low locations e5 , and the average value is taken as the number of cumulative standard axle load applications actually borne by the actual road section. S8. Cumulative action times of the equivalent design axle load of the design lane in the initial year of the section's opening to traffic According to the number of years of opening to traffic and in combination with the "Code for Design of Highway Asphalt Pavements" "JTG D50-2017", calculate the cumulative action times N1 of the equivalent design axle load of the design lane in the initial year of the section's opening to traffic. The calculation formula is shown in Equation (6); Where N e5 is the cumulative equivalent standard axle load applications of the design lanes in the investigation year (times); t1 is the number of years since the road section was opened to traffic (years); N1 is the cumulative equivalent standard axle load applications of the design lanes in the initial year when the road section was opened to traffic (times); γ is the annual growth rate of traffic volume; S9. Calculation of the cumulative standard axle load application times during the design period of the maintenance design section According to the cumulative number of equivalent single-axle loads N1 of the design lane in the initial year when the road section is opened to traffic and the number of years since the road section has been opened to traffic, the cumulative number of equivalent single-axle loads N of the design lane in the initial year of maintenance design is obtained. t1 Furthermore, the cumulative number of standard axle loads N acting during the design period of the maintenance design road section is obtained. e The calculation formula is shown in Equation (7). Where N e is the cumulative number of standard axle load applications during the design period of the maintenance design section (times); t2 is the design life (years) of the road section maintenance design; N t1 is the cumulative number of equivalent single-axle loads acting on the design lane in the initial year of the maintenance design (times); γ is the annual growth rate of traffic volume.

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