Study On Fatigue Performance Of Flexible Base Asphalt Pavement Under Accelerated Loading By HVS

Fatigue damage is one of the main forms of asphalt pavement damage in China,and it is also an important factor in the design of asphalt pavement.When fatigue damage occurs on asphalt pavement,it will not only affect ride comfort,but also cause potential safety hazards when severe.Therefore,in order to prolong the serviceability and durability of the pavement,it is of great significance to study its fatigue damage mechanism under specific environment and load and establish a corresponding fatigue prediction model.This article originated from the Western Traffic Science and Technology Project of the Ministry of Transport(20113187721260).Based on the characteristics of materials and environment in the northwest of Inner Mongolia,four types of flexible asphalt pavement test roads were paved,and the HVS acceleration loading test was used to study the pavement fatigue performance.By embedding mechanical dynamic monitoring equipment in the test road,the mechanical response characteristics of the pavement structure are analyzed,the fatigue damage rules of the asphalt pavement with flexible base are explored,and the mechanical behavior of the asphalt pavement fatigue failure is clarified.On this basis,summed up the main influencing factors of asphalt pavement fatigue performance,innovatively introduced the influence parameters of the six-parameter three-coefficient,built a flexible base asphalt pavement fatigue prediction model,and calculated the asphalt pavement fatigue life.The main research contents and results are as follows:(1)Through real-time analysis of the dynamic response characteristics of thetensile strain at the bottom of each pavement layer during acceleration loading,it can be seen that increasing the base modulus appropriately can increase the overall bearing capacity of the pavement structure,and not only can reduce the tensile strain at the bottom of the asphalt surface layer,but also help To reduce the possibility of fatigue damage on asphalt pavement.When fatigue failure occurs on the asphalt pavement,the tensile strain at the bottom of the asphalt layer increases by approximately 2.2 times the initial value.(2)The relationship between the vertical compressive stress on the top surface of the subgrade and the axial load varies in an exponential manner.In the four types of asphalt pavement structures,the structural model C has the largest sensitivity factor of the stress axis load,which is approximately 3.1 times of the remaining pavement structure.When fatigue failure occurs on the asphalt pavement,the pressure stress at the top of the roadbed abruptly changes by about 1.3 times the initial value.For the asphalt pavement structure that is prone to fatigue failure,the method of improving the compaction degree of the roadbed should be used to improve the overall bearing capacity of the pavement structure,thereby reducing the earth pressure on the top surface of the roadbed.(3)The evolution rule of the modulus of asphalt layer during the actual load measurement is determined by the falling hammer deflection meter(FWD).The evolution rule can be divided into three stages,ie,the initial modulus increase period,the mid-stage modulus acceleration decay period,and the late modulus.In the stable decay period,the three phases accounted for 5%,20% and 58% of the total process respectively.When the asphalt pavement suffered fatigue failure,the modulus of the asphalt layer attenuated to about 35% of the initial value.(4)Based on the core idea of mechanics-endogenous-external cause,the fatigue factors such as loading mode factor,bottom layer tensile strain of asphalt layer,dynamic modulus,voidage,asphalt content,and temperature were used to combine the number of load breaks,days of adverse seasons,and lateral distribution coefficients.A model for predicting fatigue of asphalt pavement with flexible foundation was built.The fatigue life of the four asphalt pavement structures is estimated to be between 16 and 24 million times.The recommended fatigue resistance of the pavement structure is: pavementstructure D> pavement structure B> pavement structure A> pavement structure C.