Study On The Dynamic Responses Of Highway Structure Layers Under Traffic Loads And The Design Method Of Dynamic Strength

The characteristics of highway structure layers under traffic loads are different from the static mechanical conditions.However,the traffic loads are always considered as static in present theoretical analysis and design of highway.To understand and master the influence of traffic loads on the highway structure layers so as to provide some technical supports for the design of the pavement and the subgrade, in this dissertation,the dynamic responses of highway structure layers are studied systematically based on the combination of theoretical analysis,numerical calculations and the full size model experiment.The main conclusions are as follows:Firstly,the dynamic response of Continuously Reinforced Concrete Pavement (CRCP) resting on viscoelastic Winkler foundation is investigated,and the analytical solutions of CRCP under multiple-wheel loads are obtained by using the trigonometric series,Fourier transform and the superposition method.Numerical results are derived when the horizontal resistance at the foundation's bottom is considered,and the influence of various parameters such as the loads,pavement and foundation parameters on the dynamic responses is performed.To evaluate the dynamic responses of rough pavement subjected to traffic loads,research is focused on the geometric roughness of pavement,and by regarding the pavement roughness as sine function and simplifying the quarter vehicle to a two DOF vibration system,the analytical and numerical results of pavement are obtained and used to analyze the influence of moving load velocity,rough pavement parameters and foundation parameters on the dynamic displacement responses.Secondly,the three dimensional multiple layered ground model are established based on the elastic dynamic theory and Biot's dynamic equation.Dynamic responses of rigid pavement and flexible pavement resting on the layered ground are studied respectively.By employing transfer matrix method,the integrated rigid matrix of multiple layered ground is obtained.The vehicle loads are considered as rectangular harmonic moving loads,and the analytical solution of the pavement and layered ground interaction is deduced with Lame decomposition theorem of displacement field and Fourier transform method.By employing IFFT,the influence law is studied using numerical analysis which concerns the influence of the factors(velocity, frequency of moving loads,permeability coefficient,the depth of elastic soil layer and the rigidity ratio between elastic single-phase layer and saturated layer) to the distribution of the foundation's vertical displacement and pore pressure.Thirdly,the thermodynamic responses of porous elastic medium subjected to time harmonic loads are investigated analytically in the context of the theory of linear thermoelastic.The material of foundation,obeying Biot's dynamic poroelastic theory, is idealized as a uniform,fully saturated poroelastic half-space stratum.The coupling thermo-hydro-mechanical dynamic governing equations are derived by employing Biot's dynamic poroelastic theory and linear thermoelastic theory.The analytical solutions in the form of integral of stress,displacement,temperature distribution and excess pore water pressure are obtained by using Fourier transform.Numerical results are obtained to analyze the differences among coupling thermo-hydro-mechanical dynamic theory(THMD),coupling hydro-mechanical dynamic theory(HMD) and thermo-elastic dynamic theory(TMD).Fourthly,full size laboratory model experiment is conducted based on the construction of highway.The variation of the dynamic stress and strain and total deformation of highway structure layers is discussed under the condition of two subgrade soil including full weathering granite and cement stable soil.The results of laboratory model experiment are consistent with that of theoretical analysis.Further discussion is performed on the effect of the modulus and depth of pavement to the dynamic responses.Finally,combining the theoretical analysis,laboratory model experiment and the accumulative deformation model established though the cyclic triaxial tests on soft clay,an approach is presented to calculate the long-term settlements of soft ground induced by traffic loadings.Numerical results are obtained to analyze the influence of the characteristics of highway structure layers on long-term settlements.Moreover,a new method for design of highway subgrade is proposed to fit the depth and dynamic strength of subgrade considering compatibility of deformation between pavement and subgrade and three typical pavement structure are designed for illustration using this method.