Mechanical Response And Crack Propagation Analysis Of Asphalt Overlay Under Load And Seepage Coupling

As an effective structural reinforcement measure,asphalt overlay is widely used in the pavement reconstruction design of expressways and urban roads.However,under the comprehensive action of traffic load and environmental factors,the original pavement structure and materials will produce irreversible decay,resulting in all kinds of early damage when the pavement after overlay and reconstruction often fails to reach the design life,At the same time,the existence of water not only affects the cohesion of asphalt mixture,but also changes the internal stress state of pavement structure.Therefore,it is of great significance to study the mechanical characteristics of asphalt pavement under the coupling action of seepage field and stress field under different overhaul schemes for the design and selection of asphalt pavement reconstruction in our country.Based on the reconstruction project of Gaoming Avenue in the first ring road of Foshan,based on the saturated porous medium theory and Biot consolidation theory,this paper establishes the finite element model of asphalt overlay pavement with different milling schemes with the help of ABAQUS software.Firstly,the spatial distribution and time-varying law of mechanical response of saturated direct overlay asphalt pavement under dynamic load are studied;Then,according to different milling methods,the effects of overlay and back paving material parameters on the mechanical indexes of overlay asphalt pavement are discussed.On this basis,the effects of material parameters and driving load on pore water pressure and other mechanical fields are further analyzed by orthogonal design method;Finally,the crack propagation law of the old asphalt layer of overlay asphalt pavement under the coupling action of traffic load and hydrodynamic pressure is quantitatively analyzed.The results show that:under the action of dynamic load,the pore water pressure in the overlay asphalt pavement changes alternately,and it is large at the junction of the old asphalt layer and the original pavement base.This part is significantly scoured and pumped by dynamic water pressure.As the load changes with time,the mechanical fields in the pavement structure,such as vertical displacement,vertical stress,longitudinal stress and maximum shear stress,also show obvious fluctuation.The mechanical response of old and new Pavements under load seepage coupling is very different before and after overlay.The pore water pressure in the old pavement asphalt layer before overlay is greater than that in the new pavement asphalt layer before overlay;After the overlay and reconstruction of asphalt concrete layer,it can effectively reduce the vertical deformation of the whole pavement structure,reduce the longitudinal tensile stress at the bottom of the original pavement base and improve the shear condition between the asphalt layer and the original base layer,but it will increase the pore water pressure and tensile strain at the bottom of the old asphalt layer.The elastic modulus,permeability coefficient,vehicle axle load and speed of overlay and back overlay materials will affect the mechanical response of overlay asphalt pavement.The larger the modulus and permeability coefficient of asphalt layer,the more conducive to reduce the pore water pressure of asphalt layer.The influence degree of each factor on each mechanical index is different,among which the permeability coefficient of the back paving material has the greatest influence on the pore water pressure in the asphalt layer,and the tensile strain at the bottom of the overlay is mainly affected by the elastic modulus of the back paving layer;Overload is the main influencing factor of other mechanical indexes.Compared with the single action of load,the existence of pore water pressure will promote the tensile propagation of cracks without affecting the shear propagation of cracks.Under the coupling action of load and seepage,the cracks at the bottom of the old asphalt layer mainly expand in the form of shear.The increase of the elastic modulus of the asphalt layer and the axle load of the vehicle are not conducive to inhibiting the development of cracks.When the thickness of the overlay increases and the elastic modulus of the old road base is large,it can delay the development of cracks to a certain extent.