Fatigue damage prediction method of full flexible asphalt pavement structure under multi-axle group load

Abstract

The application discloses a method for predicting fatigue damage of full-flexibility asphalt pavement structure under multi-axle group load, and belongs to the technical field of pavement damage prediction. The method comprises the following steps: determining the bending stiffness modulus of each layer of asphalt mixture of the asphalt pavement under the design condition; combining the fatigue performance test of the material under the multi-temperature and multi-strain level of the structure checking layer position to build a fatigue cracking life prediction model of the asphalt mixture layer of the pavement structure; determining the cumulative heavy vehicle traffic volume, the axle load action times and the action times of different load levels of each axle group of the design lane within an analysis period; calculating the fatigue damage times of the pavement structure under different axle group loads; determining the cumulative fatigue damage of the asphalt pavement structure under the heavy vehicle traffic volume within the analysis period; and finally determining the allowable heavy vehicle traffic volume of the pavement structure. The application can better predict the fatigue damage of the asphalt pavement structure in combination with the multi-axle group load, and provides important guidance for the precise design and maintenance and repair of the pavement structure.

Description

Technical Field

[0001] This invention discloses a method for predicting fatigue damage of fully flexible asphalt pavement structures under multi-axis loads, belonging to the field of pavement damage prediction technology. Background Technology

[0002] With the rapid development of the national economy and highway transportation, high speed and heavy load have become the development trend of road traffic. The dynamic load of heavy vehicles on the road surface is a major cause of early road surface damage, and the static design method for highways is increasingly unable to meet the requirements. Studying the dynamic behavior of the road surface under vehicle load, revealing the failure mechanism of the road surface, and promoting the transformation of road surface structure design from static to dynamic has become one of the hot research issues in the road industry. At present, when solving for road surface damage, due to the complexity of theoretical analysis and numerical calculation, road workers generally simplify the vehicle load to the equivalent standard axle load, which deviates significantly from the actual traffic load pattern. At the same time, the influence of actual vehicle speed, temperature and other environmental factors is not considered, resulting in a serious discrepancy between the fatigue damage of the road surface structure and the actual situation, leading to inaccuracies in the design and maintenance of asphalt pavement structures and affecting the service life of asphalt pavement structures. Summary of the Invention

[0003] The purpose of this invention is to provide a method for predicting fatigue damage to fully flexible asphalt pavement structures under multi-axle loads, so as to solve the problem that the impact of vehicle loads on the fatigue damage of pavement structures is difficult to determine in the prior art.

[0004] A method for predicting fatigue damage to fully flexible asphalt pavement structures under multi-axis loading includes:

[0005] S1. Initially propose the pavement structure combination and determine the flexural stiffness modulus Ed of each asphalt mixture layer under the design conditions;

[0006] S2. Based on the flexural stiffness modulus of each asphalt mixture layer in S1, and combined with the fatigue performance test of the material under multiple temperature and strain levels in the structural verification layer, a fatigue cracking life prediction model for asphalt mixture layers in pavement structures is constructed.

[0007] S3. Obtain road traffic load parameters using the on-site dynamic weighing system to determine the cumulative heavy vehicle traffic volume and axle load application frequency of the design lane during the analysis period;

[0008] S4. Determine the number of times different load levels apply to each axle group based on traffic load parameters;

[0009] S5. Use road mechanics calculation software to calculate and determine the bending tensile strain at the bottom of the asphalt layer under different axle group load levels;

[0010] S6. Based on the fatigue cracking life prediction model of asphalt mixture layer of pavement structure and the bending tensile strain of the bottom layer of asphalt layer under different axle group load levels, calculate the number of fatigue failures of pavement structure under different axle group loads.

[0011] S7. Construct a fatigue damage model for asphalt pavement structure to determine the cumulative fatigue damage of asphalt pavement structure under heavy vehicle traffic during the analysis period.

[0012] S8. Based on the cumulative fatigue damage of the asphalt pavement structure obtained in S7, determine the allowable heavy vehicle traffic volume of the pavement structure.

[0013] The design conditions for S1 include: design temperature, design frequency, and field service void ratio.

[0014] The measured temperature field data of typical asphalt pavement in the project area are obtained by using a pavement structure temperature measurement device. The calculation model of temperature at different depths of the pavement is obtained by using the least squares method. Then, the equivalent temperature of the target structural layer thickness of the asphalt pavement is determined and the equivalent temperature is used as the design temperature.

[0015] The fatigue cracking life prediction model for asphalt mixture layers was determined by four-point bending fatigue tests. Four-point bending fatigue tests were conducted on different types of asphalt mixtures. Based on the fatigue life results of asphalt mixtures under different test temperatures and strain levels, fatigue life prediction models for different types of asphalt mixtures were derived.

[0016]

[0017] Obtain a fatigue cracking life prediction model for asphalt mixture layers:

[0018]

[0019] In the formula, N lab The fatigue life (times) of the asphalt mixture flexural fatigue test specimen at failure; E lab ε represents the flexural stiffness modulus (MPa) at the test frequency and test temperature; lab The strain (με) of the four-point bending fatigue test; N f The fatigue cracking life (times) of the asphalt mixture layer; E d ε is the design flexural stiffness modulus (MPa) of the asphalt mixture layer material; ε is the flexural tensile strain (με) at the bottom of the asphalt mixture layer, which is determined by pavement structure mechanics software; k1~k5 are fitting parameters, which are obtained by solving the fatigue life prediction model of the asphalt mixture and then substituted into the fatigue cracking life prediction model of the asphalt mixture layer; β is the fatigue cracking reliability factor of the asphalt mixture layer, which is determined by the highway grade and traffic volume.

[0020] The S4 axle sets include single axle single tire, single axle dual tire, dual axle single tire, dual axle dual tire, triple axle dual tire, and quadruple axle dual tire.

[0021] The calculation and determination of the asphalt layer bottom tensile strain under different axle group load levels using pavement mechanics calculation software includes: firstly, calculating the asphalt layer bottom flexural tensile strain under single-axle single-tire and single-axle dual-tire conditions using pavement mechanics calculation software; then, determining the asphalt layer bottom flexural tensile strain ε for all axle group loads in the traffic load distribution according to the following formula. ij :

[0022] For single-axle single-tire:

[0023] For single-axle dual tires: Where, ε ij Let L be the tensile strain (με) at the bottom of the asphalt layer caused by a uniaxial load of type i shaft group under load level j; ij The j-th load is applied to shaft group i; n is the number of individual shafts in shaft group i; ε SS,53 The flexural tensile strain (με) at the bottom of the asphalt layer when a load of 53 kN is applied to a single axle and single tire; ST,100 The bending tensile strain (με) at the bottom of the asphalt layer when a load of 100kN is applied to a single-axle dual tire;

[0024] Calculate the number of fatigue failures N of the pavement structure under different axle group loads. ij include:

[0025]

[0026] In the formula, N ij The number of fatigue failures of pavement structure for type i axle group under load level j; n is the number of axles in type i axle group; β is the fatigue cracking reliability factor of asphalt mixture layer, determined by highway grade and traffic volume; E d The design flexural stiffness modulus (MPa) of the asphalt mixture layer is determined by S1; ε ij ε represents the bending tensile strain (με) at the bottom of the asphalt layer caused by uniaxial load of type i shaft group under level j load; k1~k5 are fitting parameters.

[0027] In S7, the fatigue damage of the pavement structure under different axle groups and different load levels is determined. The sum of the fatigue damage of the pavement structure caused by different loads on each axle group is the cumulative fatigue damage of the pavement structure under the cumulative heavy vehicle traffic volume. The fatigue damage calculation model D for asphalt pavement structure is:

[0028]

[0029] Where, d ij The fatigue damage of pavement structure for type i axle group under level j load; eij N represents the cumulative number of times a heavy vehicle operates under load level j in axis group i; ij Let be the number of fatigue failures of the pavement structure for type i axle group under load level j.

[0030] Compared with the prior art, the present invention has the following advantages: it can better predict the fatigue damage of asphalt pavement structure by combining multi-axle group loads, and can obtain the number of fatigue failures of pavement structure under different loads for different axle groups. Attached Figure Description

[0031] Figure 1 It is the master curve of flexural stiffness modulus of SMA-13, AC-20, AC-25, LSPM-25 and AC-13F asphalt mixtures at a reference temperature of 20℃. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0033] A method for predicting fatigue damage to fully flexible asphalt pavement structures under multi-axis loading includes:

[0034] S1. Initially propose the pavement structure combination and determine the flexural stiffness modulus Ed of each asphalt mixture layer under the design conditions;

[0035] S2. Based on the flexural stiffness modulus of each asphalt mixture layer in S1, and combined with the fatigue performance test of the material under multiple temperature and strain levels in the structural verification layer, a fatigue cracking life prediction model for asphalt mixture layers in pavement structures is constructed.

[0036] S3. Obtain road traffic load parameters using the on-site dynamic weighing system to determine the cumulative heavy vehicle traffic volume and axle load application frequency of the design lane during the analysis period;

[0037] S4. Determine the number of times different load levels apply to each axle group based on traffic load parameters;

[0038] S5. Use road mechanics calculation software to calculate and determine the bending tensile strain at the bottom of the asphalt layer under different axle group load levels;

[0039] S6. Based on the fatigue cracking life prediction model of asphalt mixture layer of pavement structure and the bending tensile strain of the bottom layer of asphalt layer under different axle group load levels, calculate the number of fatigue failures of pavement structure under different axle group loads.

[0040] S7. Construct a fatigue damage model for asphalt pavement structure to determine the cumulative fatigue damage of asphalt pavement structure under heavy vehicle traffic during the analysis period.

[0041] S8. Based on the cumulative fatigue damage of the asphalt pavement structure obtained in S7, determine the allowable heavy vehicle traffic volume of the pavement structure.

[0042] The design conditions for S1 include: design temperature, design frequency, and field service void ratio.

[0043] The measured temperature field data of typical asphalt pavement in the project area are obtained by using a pavement structure temperature measurement device. The calculation model of temperature at different depths of the pavement is obtained by using the least squares method. Then, the equivalent temperature of the target structural layer thickness of the asphalt pavement is determined and the equivalent temperature is used as the design temperature.

[0044] The fatigue cracking life prediction model for asphalt mixture layers was determined by four-point bending fatigue tests. Four-point bending fatigue tests were conducted on different types of asphalt mixtures. Based on the fatigue life results of asphalt mixtures under different test temperatures and strain levels, fatigue life prediction models for different types of asphalt mixtures were derived.

[0045]

[0046] Obtain a fatigue cracking life prediction model for asphalt mixture layers:

[0047]

[0048] In the formula, N lab The fatigue life (times) of the asphalt mixture flexural fatigue test specimen at failure; E lab ε represents the flexural stiffness modulus (MPa) at the test frequency and test temperature; lab The strain (με) of the four-point bending fatigue test; N f The fatigue cracking life (times) of the asphalt mixture layer; E d ε is the design flexural stiffness modulus (MPa) of the asphalt mixture layer material; ε is the flexural tensile strain (με) at the bottom of the asphalt mixture layer, which is calculated and determined by pavement structure mechanics software; k1~k5 are fitting parameters, which are obtained by solving the fatigue life prediction model based on different types of asphalt mixtures, and then substituted into the fatigue cracking life prediction model of the asphalt mixture layer; β is the fatigue cracking reliability factor of the asphalt mixture layer, which is determined by the highway grade and traffic volume.

[0049] The S4 axle sets include single axle single tire, single axle dual tire, dual axle single tire, dual axle dual tire, triple axle dual tire, and quadruple axle dual tire.

[0050] The calculation and determination of the asphalt layer bottom tensile strain under different axle group load levels using pavement mechanics calculation software includes: firstly, calculating the asphalt layer bottom flexural tensile strain under single-axle single-tire and single-axle dual-tire conditions using pavement mechanics calculation software; then, determining the asphalt layer bottom flexural tensile strain ε for all axle group loads in the traffic load distribution according to the following formula. ij :

[0051] For single-axle single-tire:

[0052] For single-axle dual tires: Where, ε ij Let L be the tensile strain (με) at the bottom of the asphalt layer caused by a uniaxial load of type i shaft group under load level j; ij The j-th load is applied to shaft group i; n is the number of individual shafts in shaft group i; ε SS,53 The flexural tensile strain (με) at the bottom of the asphalt layer when a load of 53 kN is applied to a single axle and single tire; ST,100 The bending tensile strain (με) at the bottom of the asphalt layer when a load of 100kN is applied to a single-axle dual tire;

[0053] Calculate the number of fatigue failures N of the pavement structure under different axle group loads. ij include:

[0054]

[0055] In the formula, N ij The number of fatigue failures of pavement structure for type i axle group under load level j; n is the number of axles in type i axle group; β is the fatigue cracking reliability factor of asphalt mixture layer, determined by highway grade and traffic volume; E d The design flexural stiffness modulus (MPa) of the asphalt mixture layer is determined by S1; ε ij ε represents the bending tensile strain (με) at the bottom of the asphalt layer caused by uniaxial load of type i shaft group under level j load; k1~k5 are fitting parameters.

[0056] In S7, the fatigue damage of the pavement structure under different axle groups and different load levels is determined. The sum of the fatigue damage of the pavement structure caused by different loads on each axle group is the cumulative fatigue damage of the pavement structure under the cumulative heavy vehicle traffic volume. The fatigue damage calculation model D for asphalt pavement structure is:

[0057]

[0058] Where, d ij The fatigue damage of pavement structure for type i axle group under level j load; e ij N represents the cumulative number of times a heavy vehicle operates under load level j in axis group i; ij Let be the number of fatigue failures of the pavement structure for type i axle group under load level j.

[0059] The design temperature is:

[0060] T′=α5×z 5 +α4×z 4 +α3×z 3 +α2×z 2 +α1×z+α0;

[0061] In the formula, T′ is the actual measured temperature (°C), α5, α4, α3, α2, α1, and α0 are model parameters, z is the thickness of the asphalt surface layer (cm), and the bottom of the asphalt layer is taken as the starting point.

[0062] The equivalent temperature of each structural layer of the asphalt pavement is determined as the design temperature using the following formula:

[0063]

[0064] In the formula, T di h represents the equivalent temperature (°C) of each structural layer of the asphalt surface course. i Let be the thickness (cm) of each structural layer of the asphalt pavement, and i be the number of structural layers of the asphalt pavement, i = 1, 2, 3...n. When i = 1, h = 0.

[0065] The design frequency is:

[0066] Among them, f d The loading frequency (Hz) of the vehicle load on the target structural layer of the asphalt pavement at the design speed is given by h, which is the depth of the road surface downwards (cm), and v is the design speed of the loaded vehicle (km / h).

[0067] In S1, the flexural stiffness modulus of asphalt mixture is determined by a four-point flexural fatigue test. The test measures the flexural stiffness modulus of asphalt mixture at different test temperatures and loading frequencies. Based on the time-temperature substitution principle, a master curve for the flexural stiffness modulus of asphalt mixture is established. First, the flexural stiffness modulus at the design temperature and heavy vehicle design speed is determined. Then, the porosity modulus (3%–5.0%) of the asphalt mixture in the indoor test is adjusted to the service porosity modulus. This is the design flexural stiffness modulus E for each layer of asphalt pavement. d Typical service void ratios for asphalt mixtures are as follows: AC-7, AC-10, and AC-13: 5.0%; AC-13F: 4.0%; AC-16, AC-20, and AC-25: 7%; SMA-10, SMA-13, and SMA-14: 4.0%; LSPM-25: 17%; EME-14: 3.5%; and EME-20: 4.5%.

[0068] Adjust the porosity modulus of asphalt mixtures in laboratory tests to the predicted modulus using the following formula:

[0069]

[0070] Taking a newly built expressway in Jinan, Shandong Province as an example, the fatigue life of the asphalt mixture layer of the expressway pavement is determined using the method proposed in this invention.

[0071] The pavement structure is a full-thickness asphalt concrete pavement structure, which is a typical fully flexible asphalt pavement structure. The full-thickness asphalt pavement structure is to directly lay an asphalt mixture layer on the top surface of the subgrade. The asphalt layer thickness is 380mm, and the target reliability of the pavement structure is 97%.

[0072] Asphalt mixture samples were prepared. Typical service void ratios for asphalt mixtures were as follows: AC-7, AC-10, and AC-13: 5.0%; AC-13F: 4.0%; AC-16, AC-20, and AC-25: 7%; SMA-10, SMA-13, and SMA-14: 4.0%; LSPM-25: 17.0%; EME-14: 3.5%; and EME-20: 4.5%. In this invention, the test void ratios selected were: SMA-13 ​​(3.8%), AC-20 (5.0%), AC-25 (5.0%), LSPM-25 (15.0%), and AC-13F (2.4%).

[0073] The test temperatures were set at 5, 10, 20, 30, and 40℃, and the test frequencies at each temperature were 0.1, 0.2, 0.5, 1, 5, 10, 20, and 25Hz. The test results are shown in Table 1. The master curves for the flexural stiffness modulus of the asphalt mixture in each structural layer of the asphalt layer were established, as shown in Table 1. Figure 1 .

[0074] Table 1. Test results of flexural stiffness modulus

[0075]

[0076] Based on the master curve of the flexural stiffness modulus of asphalt mixtures, the calculation model of the flexural stiffness modulus of asphalt mixtures in each structural layer of the asphalt layer under different temperatures and loading frequencies is obtained, as shown below:

[0077]

[0078] Where: E1 is the flexural stiffness modulus of the upper SMA-13 ​​layer (MPa); T1 is the thickness equivalent temperature of the upper layer; f1 is the loading frequency of the upper layer (Hz);

[0079]

[0080] Where: E2 is the flexural stiffness modulus (MPa) of the intermediate layer AC-20; T2 is the thickness equivalent temperature of the intermediate layer; f2 is the loading frequency (Hz) of the upper layer;

[0081]

[0082] Where: E3 is the flexural stiffness modulus of the lower layer AC-25 (MPa); T3 is the thickness equivalent temperature of the lower layer; f3 is the loading frequency of the lower layer (Hz);

[0083]

[0084] Where: E4 is the flexural stiffness modulus (MPa) of the flexible base layer LSPM-25; T4 is the equivalent temperature of the lower layer thickness; f4 is the loading frequency (Hz) of the lower layer;

[0085]

[0086] Where: E5 is the flexural stiffness modulus (MPa) of fatigue layer AC-13F; T5 is the equivalent temperature of fatigue layer thickness; f5 is the loading frequency (Hz) of the underlying layer;

[0087] The equivalent temperatures of each structural layer of the asphalt pavement are determined as follows:

[0088]

[0089] Wherein: T d1 The equivalent temperature of the upper SMA-13 ​​layer is given by z, and the thickness of the asphalt surface layer is given by z. The origin is set at the bottom of the asphalt layer (cm).

[0090]

[0091] Wherein: T d2 The equivalent temperature of the AC-20 intermediate layer is given by z, and the thickness of the asphalt surface layer is given by z. The origin is set at the bottom of the asphalt layer (cm).

[0092]

[0093] Wherein: T d3 Let z be the equivalent temperature of the lower AC-25 layer, z be the coordinate of the asphalt surface layer thickness, and the origin be the bottom of the asphalt layer (cm).

[0094]

[0095] Wherein: T d4 The equivalent temperature of the flexible base layer LSPM-25 is given by z, which is the coordinate of the asphalt surface layer thickness. The origin is set at the bottom of the asphalt layer (cm).

[0096]

[0097] Wherein: T d5 The equivalent temperature of the fatigue layer AC-13F is given by z, and the thickness coordinate of the asphalt surface layer is given by z. The origin is set at the bottom of the asphalt layer (cm).

[0098] The calculated equivalent temperatures of the thicknesses of the asphalt pavement structure's top, middle, bottom, flexible base, and fatigue layers are 50.5℃, 47.5℃, 43.3℃, ​​35.2℃, and 32.6℃, respectively.

[0099] By setting up a dynamic weighing system on the asphalt pavement surface and obtaining the design speed of a heavy vehicle at 100 km / h, the loading frequencies of the asphalt pavement structure's top layer, middle layer, bottom layer, flexible base layer, and fatigue layer were found to be 12 Hz, 10 Hz, 7 Hz, 6.5 Hz, and 5 Hz, respectively.

[0100] Based on the calculation model of the flexural stiffness modulus of asphalt mixture, the flexural stiffness moduli of SMA-13, AC-20, AC-25, LSPM-25 and AC-13F under the design temperature and heavy vehicle design speed are determined to be 1287MPa, 2662MPa, 2272MPa, 2307MPa and 4190MPa, respectively.

[0101] Adjusting the test porosity modulus of SMA-13, AC-20, AC-25, LSPM-25, and AC-13F to their service porosity modulus, the test porosities of SMA-13, AC-20, AC-25, LSPM-25, and AC-13F are 3.8%, 5.0%, 5.0%, 15%, and 2.4%, respectively. The engineering implementation service porosities are 4.0%, 7.0%, 7.0%, 17.0%, and 4.0%, respectively. Therefore, the service porosity moduli of SMA-13, AC-20, AC-25, LSPM-25, and AC-13F are 1216 MPa, 2329 MPa, 1988 MPa, 1538 MPa, and 3830 MPa, respectively.

[0102] AC-13F asphalt mixture was prepared and subjected to flexural fatigue tests. A total of 27 specimens were tested at three different temperatures: 10°C, 20°C, and 30°C, with nine specimens at each temperature. The nine specimens at each temperature were averaged across three strain levels, and the test frequency was 10 Hz. The test results are shown in Table 2.

[0103] Table 2 Results of AC-13F Bending Fatigue Test

[0104]

[0105] Based on the experimental results in the table, the fatigue prediction model for AC-13F is as follows:

[0106]

[0107] The fatigue life prediction model for asphalt pavement structures is as follows:

[0108]

[0109] Road traffic load parameters were obtained using an on-site dynamic weighing system. The number of load cycles applied to all axle groups during the 30-year analysis period for heavy vehicle traffic was 1.24 × 10⁻⁶. 8 The traffic load distribution is shown in Table 3 below.

[0110] Table 3 Traffic Load Distribution

[0111]

[0112] Table 4 Number of load applications for different axle groups during the 30-year analysis period

[0113]

[0114] The tensile strain at the bottom of the asphalt layer under different axle group load levels was calculated using the pavement mechanics calculation software BISAR3.0. First, the flexural tensile strain at the bottom of the asphalt layer under single-axle single-tire and single-axle dual-tire loads was calculated, as shown in Table 5. Then, the flexural tensile strain at the bottom of the asphalt layer under all axle group loads in the traffic load distribution was determined according to the following formula, as shown in Table 6.

[0115] For single-axle single-tire:

[0116] For single-axle dual tires:

[0117] Table 5. Bending tensile strain at the bottom of asphalt layer under single-axle single-tire and single-axle dual-tire conditions.

[0118] Shaft group type Axle load (kN) Vertical load (kPa) Maximum bending tensile strain (με) Single axle single tire 53 800 77.8 Single-axle dual tire 100 700 132.6

[0119] Table 6. Bending tensile strain at the bottom of the asphalt layer under different shaft group loads.

[0120]

[0121] Based on the fatigue cracking life prediction model of asphalt mixture layers in pavement structures and the flexural strain ε at the bottom of the asphalt layer caused by single axle load under level j for type i axle group in Table 6, ij Calculate the number of fatigue failures N of the pavement structure under different axle group loads using the following formula. ij Based on the highway grade and target reliability of the pavement structure, the fatigue cracking reliability factor of the asphalt mixture layer was determined to be 9.0. The calculation results are shown in Table 7.

[0122]

[0123] Table 7. Number of fatigue failures of pavement structures under each axle group and load.

[0124]

[0125] The fatigue damage d of the pavement structure under different axle groups and different load levels is determined by the following formula. ij See Table 8.

[0126]

[0127] The sum of the fatigue damage to the pavement structure caused by different loads on each axle group is the cumulative fatigue damage to the pavement structure under the cumulative heavy vehicle traffic volume. The calculated total damage is 0.99, so the fatigue damage of this full-thickness asphalt pavement structure is 0.99.

[0128] Table 8 Fatigue damage of full-thickness asphalt pavement structure under different axle groups and loads.

[0129]

[0130] Based on the accumulated fatigue damage of the full-thickness asphalt pavement structure, the allowable number of load cycles for all axle groups under heavy vehicle traffic was determined to be 1.24 × 10⁻⁶. 8 / 0.99=1.25×10 8

[0131] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for predicting fatigue damage of fully flexible asphalt pavement structures under multi-axis loading, characterized in that, include: S1. Initially propose the pavement structure combination and determine the flexural stiffness modulus of each asphalt mixture layer under design conditions. ; S2. Based on the flexural stiffness modulus of each asphalt mixture layer in S1, and combined with the fatigue performance test of the material under multiple temperature and strain levels in the structural verification layer, a fatigue cracking life prediction model for asphalt mixture layers in pavement structures is constructed. S3. Obtain road traffic load parameters using the on-site dynamic weighing system to determine the cumulative heavy vehicle traffic volume and axle load application frequency of the design lane during the analysis period; S4. Determine the number of times different load levels apply to each axle group based on traffic load parameters; S5. Use road mechanics calculation software to calculate and determine the bending tensile strain at the bottom of the asphalt layer under different axle group load levels; S6. Based on the fatigue cracking life prediction model of asphalt mixture layer of pavement structure and the bending tensile strain of the bottom layer of asphalt layer under different axle group load levels, calculate the number of fatigue failures of pavement structure under different axle group loads. S7. Construct a fatigue damage model for asphalt pavement structure to determine the cumulative fatigue damage of asphalt pavement structure under heavy vehicle traffic during the analysis period. S8. Based on the cumulative fatigue damage of the asphalt pavement structure obtained in S7, determine the allowable heavy vehicle traffic volume of the pavement structure; The fatigue cracking life prediction model for asphalt mixture layers was determined by four-point bending fatigue tests. Four-point bending fatigue tests were conducted on different types of asphalt mixtures. Based on the fatigue life results of asphalt mixtures under different test temperatures and strain levels, fatigue life prediction models for different types of asphalt mixtures were derived. ； Obtain a fatigue cracking life prediction model for asphalt mixture layers: ； In the formula, The fatigue life of the asphalt mixture flexural fatigue test specimen at failure is expressed in cycles. The flexural stiffness modulus is given at the test frequency and test temperature, and the unit is MPa. The strain is measured in a four-point bending fatigue test, and the unit is... ; The fatigue cracking life of the asphalt mixture layer is expressed in cycles. The design flexural stiffness modulus of asphalt mixture layer material, in MPa; The tensile strain at the bottom of each asphalt mixture layer is expressed in units of 1. The value is determined by pavement structure mechanics software calculations; ~ To obtain the fitting parameters, the fitting parameters are solved based on the fatigue life prediction model of different types of asphalt mixtures, and then substituted into the fatigue cracking life prediction model of asphalt mixture layer. The fatigue cracking reliability factor of asphalt mixture layers is determined by the highway grade and traffic volume.

2. The method for predicting fatigue damage of fully flexible asphalt pavement structures under multi-axis loading as described in claim 1, characterized in that, The design conditions for S1 include: design temperature, design frequency, and field service void ratio.

3. The method for predicting fatigue damage of fully flexible asphalt pavement structures under multi-axis loading as described in claim 2, characterized in that, Accurately obtain measured temperature field data of typical asphalt pavement in the project area by using a pavement structure temperature measurement device, obtain a calculation model of temperature at different depths of the pavement using the least squares method, determine the equivalent temperature of the target structural layer thickness of the asphalt pavement, and use the equivalent temperature as the design temperature.

4. The method for predicting fatigue damage of fully flexible asphalt pavement structures under multi-axis loading as described in claim 3, characterized in that, The S4 axle sets include single axle single tire, single axle dual tire, dual axle single tire, dual axle dual tire, triple axle dual tire, and quadruple axle dual tire.

5. The method for predicting fatigue damage of fully flexible asphalt pavement structures under multi-axis loading as described in claim 4, characterized in that, The calculation of the flexural tensile strain at the bottom of the asphalt layer under different axle group load levels using pavement mechanics calculation software includes: First, the flexural tensile strain at the bottom of the asphalt layer under single-axle single-tire and single-axle dual-tire conditions is calculated using pavement mechanics calculation software. Then, the flexural tensile strain at the bottom of the asphalt layer for all axle loads in the traffic load distribution is determined according to the following formula. : For single-axle single-tire: For single-axle dual tires: in, The tensile strain at the bottom of the asphalt layer caused by a uniaxial load of type i shaft group under load level j is expressed in units of . ; The j-th load is applied to shaft group i; n is the number of individual shafts in shaft group i. The flexural tensile strain at the bottom of the asphalt layer when a load of 53 kN is applied to a single axle and single tire is given. The unit is... ; The flexural tensile strain at the bottom of the asphalt layer when a load of 100kN is applied to a single-axle dual-tire tire is given in units of _____. .

6. The method for predicting fatigue damage of fully flexible asphalt pavement structures under multi-axis loading as described in claim 5, characterized in that, Calculate the number of fatigue failures of pavement structures under different axle group loads. include: ； In the formula, Let be the number of fatigue failures of the pavement structure for type i axle group under load level j; n is the number of axles in type i axle group. It is the fatigue cracking reliability factor of asphalt mixture layers, which is determined by the highway grade and traffic volume. The design flexural stiffness modulus of the asphalt mixture layer determined by S1, in MPa; The tensile strain at the bottom of the asphalt layer caused by a uniaxial load of type i shaft group under load level j is expressed in units of . ; ~ These are the fitting parameters.

7. The method for predicting fatigue damage of fully flexible asphalt pavement structures under multi-axis loading as described in claim 6, characterized in that, In S7, the fatigue damage of the pavement structure under different axle groups and different load levels is determined. The sum of the fatigue damage of the pavement structure caused by different loads on each axle group is the cumulative fatigue damage of the pavement structure under the cumulative heavy vehicle traffic volume. The fatigue damage calculation model for asphalt pavement structures is described. for: ； in, The fatigue damage of the pavement structure under a load level of j for type i axle group; The cumulative number of times a heavy vehicle operates under load level j in axis group i; Let be the number of fatigue failures of the pavement structure for type i axle group under load level j.

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