| Because the asphalt pavement itself has defects such as unevenness and cracks,these defects reduce the fatigue life of asphalt pavement under the action of load.In this paper,considering the vehicle road coupling dynamic load effect caused by road roughness,the finite element method is used to calculate and analyze the dynamic response of three kinds of asphalt pavement structures:smooth without cracks,uneven without cracks and uneven with cracks.On this basis,the fatigue life of asphalt pavement is predicted by fatigue life prediction formula,and the influence of pavement structure design parameters and vehicle axle load on fatigue life is analyzed.The main research contents and conclusions are as follows:(1)The vehicle is simplified as a quarter vehicle vibration model with two degrees of freedom,and the road roughness is taken as the excitation source of the vehicle model to solve the dynamic load caused by vehicle road coupling considering the road roughness.The finite element method is used to calculate and analyze the dynamic response of two kinds of pavement structures,smooth without cracks and uneven without cracks,and to predict the fatigue life.The results show that increasing the thickness and elastic modulus of the base will increase the transverse tensile stress at the bottom of the base,and it is easy to form semi-rigid base reflection cracks.The fatigue life of crack free uneven asphalt pavement is reduced by 33.9%compared with that of smooth pavement.(2)The dynamic response of the uneven asphalt pavement with preset cracks is analyzed,the stress intensity factor at the crack tip is calculated,and the effect of pavement structure design parameters and vehicle axle load is analyzed.The results show that the crack propagation in the early stage is mainly caused by the open stress intensity factor K1,and the crack propagation in the middle and late stage is caused by the joint action of the open stress intensity factor K1 and the shear stress intensity factor K2,and K2 is greater than K1 at the end of the crack;The thickness and K value of surface course and base course are negatively correlated,K1 and K2 are positively correlated with surface course modulus and negatively correlated with base course modulus;Overload has the most obvious effect on K1 and K2.(3)According to the above calculation results,based on Paris formula,the fatigue life of asphalt pavement is calculated and analyzed by linear approximation method.The results show that increasing the thickness of surface course and base course is the most effective method to improve the service life of asphalt pavement,and the influence of base course thickness is small;The fatigue life is negatively correlated with the modulus of the surface course,and increasing the modulus of the base course can improve the service life of the pavement;When the axle load increases by 100%,the fatigue life decreases by 243%;The sensitivity order of the four material parameters affecting the fatigue life of asphalt pavement is surface layer thickness>base layer thickness>surface layer modulus>base layer modulus.(4)Based on the statistics of the traffic volume of different types of vehicles on Guanzhong Ring Road(S107)and the calculation and analysis of axle load conversion method,the results show that the fatigue failure time of asphalt pavement is reduced by 33.7%due to the unevenness of pavement,and under the action of positive load and partial load,It takes 3.93-4.78 years for the cracks in the base of the uneven pavement to penetrate the surface. |
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