| With the deepening of the study on the properties of asphalt mixture,the mechanism of the viscoelastic-plastic property,rutting and fatigue cracking of asphalt pavement are gradually clarified.However,for a long time,the analytical method of asphalt pavement structure analysis remains at the theoretical stage of multilayered elasticity and viscoelastic system.Although finite element method and discrete element method can describe the damage process of specific asphalt pavement structure well,their complicated analysis process cannot be extended to engineering practice.To solve the limitations of traditional pavement mechanics theory,introducing energy principle into asphalt pavement structure analysis,to establish a universal energy system of asphalt pavement.From the perspective of energy,analyzing the causes of asphalt pavement damage more detailed.Ensuring that the calculation results can better relate to engineering practice.Meanwhile,the theoretical system can be applied in asphalt pavement design method.Firstly,based on the energy principle and the classical theories of viscoelastic mechanics and elastic-plastic mechanics,the transformation process of load work in asphalt pavement structure is analyzed.The causes of elastic strain energy,plastic dissipated energy and creep dissipated energy and their basic calculation methods are clarified.In three-dimensional state,by combining the constitutive equation of asphalt mixture,the energy equation of asphalt pavement is deduced,and the asphalt energy system is established.Combined with multilayered viscoelastic system,according to each part of the energy equation,the calculation program is written.Under single axisymmetric halfspace,double layer system and double axisymmetric viscoelastic double layer system,the distribution and diffusion forms of energy in pavement structure are analyzed.Verifying the correctness of asphalt pavement energy system from two aspects of numerical calculation and engineering practice.The results show that the work done by load is mainly converted into elastic strain energy which can be completely recovered generally.Creep dissipated energy mainly accumulates near the load surface and reaches its peak value at the center of the track.Plastic dissipated energy is mainly distributed in asphalt layer and its peak value appeared 2~3cm below the center of wheel track.Creep dissipated energy diffuses downward in a wavy form,mainly causing the vertical permanent deformation of asphalt pavement.Plastic dissipated energy mainly diffuses horizontally in a circular form,mainly causing plastic shear flow deformation of asphalt pavement.To reflect the working state of asphalt pavement under different environments,the changes of energy under horizontal load,overload,temperature and material properties are analyzed.The results show that all energies are concentrated near the road surface under horizontal load,and plastic dissipated energy is almost equal to elastic strain energy.That is,horizontal load mainly causes asphalt pavement shape change.In general,the horizontal load coefficient is small and the energy input from horizontal load to asphalt pavement can be ignored.However,under special conditions such as steep slope section,horizontal load will lead to a large increase of plastic dissipated energy near the road surface and reinforces plastic shear failure.Under the condition of overload,the energy distribution and diffusion form have not changed,but the energy value increased significantly,and the failure of asphalt pavement appears in advance.The properties of asphalt mixture are different at different temperatures so that the proportions of the energies will change.At low temperature,asphalt pavement tends to be completely elastic.All energy values are low and creep dissipated energy is almost zero.At normal temperature,asphalt pavement enters into low viscoelastic state,showing that total energy and elastic strain energy increase greatly with the increasing temperature,but the creep dissipated energy changes little.At high temperature,asphalt pavement enters into high viscoelastic state,showing that creep dissipated energy increases greatly,but elastic strain energy hardly changed any more.Finally,the connection between asphalt pavement energy system and engineering practice is established.Based on Mises distortion yield limit,a method of calculating plastic dissipated energy yield limit of asphalt pavement is presented,and verifying the results based on the results of direct tensile test.Based on the above energy calculation and analysis results,the actual plastic failure zone and main creep deformation zone of asphalt pavement are analyzed under different circumstances.In the end,the optimal thickness of asphalt layer is calculated by controlling the minimum energy dissipation of asphalt pavement.On the basis of many classical theories,the asphalt pavement energy system is established and can be popularized.The correctness of this method is verified by corresponding calculation and analysis.Showing its advantages over the existing theoretical system of pavement mechanics.It can promote the design method of asphalt pavement structure. |
