The Investigations For The Mechanical Behaviors Of Asphalt Pavement Considering The Interlayer Conditions

Asphalt pavement is a multi-layer structure composed of surface layer,base layer,subbase layer and subgrade.The contact surface between any two adjacent layers was defined as interlayer interface.It is assumed that the interface between adjacent layers was in a completely continuous state,and the ideal elastic layer system mechanical model was adopted,according to P.R.China's current pavement structure design specifications.However,due to the intrinsic property differences between the materials in different pavement layers and the differences of construction orders,the interlayer connections of the pavement structure were neither completely continuous nor completely smooth,but normally in a condition between these two extreme conditions.In addition,when evaluating asphalt pavement,the assumption of completely continuous state was applied for most asphalt pavement.Thus there is significant difference between the back calculated modulus and the actual modulus.Furthermore,there is no mature method to evaluate interlayer conditions.It is necessary to study the impact of interlayer conditions on the service life and performance of the road,and to establish the asphalt pavement evaluation method with the contact condition considered.This study fully considered the effect of the different interlayer conditions on the mechanical performance of pavement.Both analytical method and numerical analysis method were adopted to study the influence of interlayer contact state on the mechanical response of the pavement.Both modulus back calculation and interlayer state evaluation method were established based on artificial neural network.The main research conclusions obtained as follows:Based on the theory of the layer system and integral transformation,the mechanical response solution of the isotropic and transversely isotropic layer system under complete continuous or complete smooth conditions under static load and dynamic load were derivated.The traditional layer elastic system theory was enriched and developed.The results concluded that the stiffness of the pavement structure was smaller for completely smooth layer state than the overall stiffness of the continuous model,and the mechanical parameters were decreased significantly.In addition,the transversely isotropic properties of the structural material had impact on the mechanical response of the pavement.The smallerthe transversely isotropic coefficient is,the worse the bearing capacity performance of the pavement.The influence of surface layer transversely isotropic characteristic was greater than that of base layer.The mechanical response of the pavement under completely smooth contact condition was more sensitive to the change of the transversely isotropic coefficient of the structural materials.Based on the analytical method mentioned-above,the finite element software was used to establish the numerical analysis method of the pavement interlayer contact model characterized by the friction coefficient.The influence of the interfacial contact condition and the transverse characteristics of the material on the mechanical response of the pavement were studied.The results concluded that the contact conditions had great influence on the mechanical response of the asphalt pavement.The overall strength of the pavement structure was decreased when the contact condition was bad.The deflection of the pavement and the tensile stress were obviously different with those parameters under completely continuous condition.Then the service life of the pavement structure was reduces greatly.The friction coefficient model can well characterize the contact condition between different pavement layers.When friction coefficient is less than 0.4,the interlayer contact state was bad and the indicators change significantly.When friction coefficient is close to 1,the contact between different layers was good,the index kept stable.When f is bigger than 7,the contact was very good,the contact was close to complete continuous state.When friction coefficient is between 0.4 and 1,the interlayer contact state is normal.The horizontal force will greatly improve the shear stress value inside the pavement structure and had a great influence on the distribution of shear stress on the road surface.However,the influence of horizontal force on the surface deflection and the maximum tensile strain at the bottom of the surface was negligible.The circumstance significantly influence the properties of the asphalt surface layer materials.When the surface temperature was too high,the surface layer distributed in gradient,the modulus decreased greatly.The pavement rutting and shear failure were easier to occure by the combination of temperature and load.Considering the transverse isotropic properties of the surface layer material,it is found that with the increasing of the horizontal modulus and the vertical modulus ratio,the strength of the surface layer material was increasing and the critical mechanical indexes were improved.In addition,the dynamic response index of the same pavement structure was smaller than that under static load conditions.The pavement mechanics response under contact condition between the base layer and surface layer was more significant than the contact between the base layer and the subbase layer.Finally,the finite element software was used to establish the database of pavement surface deflection considering the interlayer contact conditions under FWD load.The optimal BP neural network inversion model was established by continuously debugging and training the learning parameters.The surface modulus and interlayer contact conditions were back calculated.The feasibility and accuracy of the algorithm were verified by the example.It is found that the interlayer condition had great influence on the pavement surface deflection.The static load deflection was significantly bigger than the dynamic deflection under the same structure conditions.The influence of the change in the interlayer contact condition on the deflection values was smaller with the increase of the distance with the loading center.The influence can be neglected when the distance was greater than 1.5m.Two kinds of bent-basin were adopted,one with 7 points with the distance from the load center is 0m,0.3m,0.6m,0.9m,1.2m,1.5 m and 2.1m,the other one with 5 points with the distance from the load center 0m,0.3m,0.6m,0.9m,1.2m.The surface modulus and interlayer contact condition back calculation results based on BP neural network was good when those two bent-basin and the thickness of the structural layer were input parameters.The back calculation accuracy of surface layer modulus was high,and the back calculation accuracy of interlayer shear parameters was slightly lower.The evaluation of the interlayer contact condition was qualitative.The laboratory testing results vertified that the optimum APAO(Amorphous Poly Alpha Olefin)content was 6%,by mass of asphalt binders,to improve the high temperature performance and anti-aging property of asphalt.In addition,three types of adhesive layer materials were applied in the oblique shear test to evaluate the shear strength of the proposed interlayer structures.The testing results concluded that the adhesive layer materials modified by 6% of APAO,by mass of asphalt binder,performed better,especially in the high temperature and aging conditions.The shear strength loss percentage of the APAO modified adhesive layer material was samller than other two.