The Fatigue Life Forecast Of Asphalt Pavement Of Graded Crushed Stone Base Based On The Finite Element Method

Compared with the traditional semi-rigid base asphalt pavement, Graded crushed stone base asphalt pavement, with the characteristic of good drainage performance and driving comfort will be further improved, the difference between the base layer and the surface layer modulus decreases,the occurrence probability of reflection crack decreased. But the mechanical strength of unbounded graded crushed stone is relatively poor than cement concrete base, the mechanical strength of graded crushed stone is mainly based on aggregate interlock behavior, forming dense framework structure, unbounded graded crushed stone can play a good role on confined condition. In this paper, through the research of experimental and theoretical simulation, optimizing the gradation types of graded crushed stone and interlayer bond types, to compensate for the lack of graded crushed stone, make full use of the advantages of good drainage performance etc. of graded crushed stone and excavate the effect of flexible base in highway construction.Through the static CBR test and resilient modulus test, concluded that the larger the maximum dry density of gradation, the greater the corresponding CBR value, the smaller the corresponding deformation rate, the greater the modulus of resilience. Based on this, through dynamic CBR test, testing the correlation coefficient of strain changes and creep modulus value with cooper pneumatic servo testing machine, the smaller the changing rate, the greater the creep modulus, the better the corresponding mechanical properties.Establishing a finite element model with the ABAQUS software, the finite element model of pavement structure from top to bottom, divided into the surface of asphalt mixture, slurry seal, penetrated oil layer(emulsified asphalt), the graded crushed stone, soil. In this simulation, the graded crushed stone is defined as D-P model, the D-P model is more appropriate to simulate the graded crushed stone with granular and non-uniformity composed of a large number discrete particles; defined the asphalt mixture surface layer and slurry seal as elastic model.Three gradation types of graded crushed stone based on test for optimization, respectively in three cases of different slurry seal thickness, applying the standard load and boundary conditions, calculating the finite element model, analyzing vertical displacement, axial stress and shear stress contrastively.Through experimental research and theoretical analysis, improving the mechanical properties of graded crushed stone base is helpful to improve the flexible base asphalt mixture paveme- nt strength and anti-deformation ability,the using of slurry seal gradation type ES-3 with more coarse particles and increasing the seal thickness appropriately are beneficial to improve the bond strength between layer and layer, graded crushed stone is more obvious between gradation types of graded crushed stone base and slurry seal thickness factors. Temperature is the non-negligible influencing factors of flexible base asphalt pavement, through the vertical displacement and stress of Mises comprehensive analysis, concluding that temperature has the minimum influence on pavement structure within the scope of 0~10 centigrade under load.In this paper, forming fatigue test specimens with self-made mold, taking 45 degree oblique shear test as the fatigue test method, the results show that the fatigue behavior is connected with the graded crushed stone base types and the interlayer bonding, estimated the fatigue life on the base of fatigue effect times through fatigue test, fitting the fatigue life prediction equation which combines the modulus of resilience of graded crushed stone base, seal thickness and interlayer stress along the direction of travel, to put forward the prediction model of fatigue life.The fitting result is conservative and ductility, with practice value and guiding significance.