Study On Structural Response Of Cement Concrete Pavement With Buffer Layer Under Dynamic Load

The proportion of cement pavement in the highway is much less than that of asphalt pavement,mainly because cement concrete pavement damage seriously in the early stage.In recent years,a large number of scholars at home and abroad proposed that the buffer layer between the base and the panel can solve this problem.As the most important functional material between the surface layer and the base layer,the mechanical properties of buffer layer are important factors affecting the quality of cement concrete road.At the same time,the response of pavement structure is actually affected by many factors such as vehicle dynamic load and temperature.Therefore,it is necessary to study the mechanical response of cement concrete pavement with buffer layer under dynamic load.The main research contents and conclusions of this paper are as follows:(1)Carry out field measurement of vehicle wheel and axle vibration acceleration on cement concrete pavement,analyze the time-domain and frequency-domain characteristics of wheel and axle vibration,and verify the necessity of mechanical response study with dynamic load.The results show that the standard deviation and resonance frequency of vibration acceleration increase with the increase of vehicle speed.The lower the grade of road smoothness,the larger the standard deviation of acceleration,and the more obvious the trend of increasing resonance frequency.When the vehicle travels at a certain speed on the cement concrete pavement,the actual vehicle load is greater than the theoretical vehicle load,so it is necessary to use dynamic load for simulation calculation in the study of the mechanical response of the pavement.(2)The specimen of"cement concrete surface layer+AC-10 buffer layer+cement stabilized gravel base layer"was made,and the interlayer shear test was carried out to analyze the binding state between the buffer layer and the surface layer and the base layer,and the interlayer binding coefficient was calculated.The results show that the interlaminar shear strength decreases with increasing temperature and increases with increasing vertical force.The interlayer bonding state is not only related to temperature,wheel load and interlayer cohesion,but also affected by interface shape,construction mode and other factors.The strength of interlayer shear strength is affected by friction resistance and bonding force.It is more reasonable to use interlayer bonding coefficient to evaluate interlayer bonding state comprehensively.(3)The creep property test of buffer layer was carried out,the creep property of buffer layer was analyzed,and the viscoelastic parameters were regressed.The results show that the strain of buffer layer increases with the increase of temperature and stress.When the temperature was 30℃,the specimens did not reach the failure stage,and the elastic deformation occurred mainly.When the temperature is 40℃and 50℃,the strain and strain rate of the specimen increase obviously,and finally reach the failure stage.The Prony series parameters,which can be directly used for simulation analysis,were calculated by using Burgers equation to regression the creep curves at different temperatures and stresses.(4)Based on the dynamic load coefficient,interlayer binding coefficient and buffer layer material parameters obtained from the field test,the finite element simulation analysis of cement concrete road with buffer layer under the action of load is carried out.The results show that the elastic modulus,thickness and vehicle speed of the buffer layer have little influence on the structural response under dynamic load,and the buffer layer thickness of 2～4cm is appropriate.The interlayer bonding coefficient has the greatest influence on the structural response,and the tensile stress tends to be stable when the bonding coefficient is greater than 20.In addition,the comprehensive coefficient k_c of fatigue equation is modified according to the calculation results of different speed and stress under shaft load.Under the action of three representative temperature cycles,the temperature inside the pavement changes with time in the form of half sine wave,and the peaks of each structural layer decrease from top to bottom and there is a hysteresis phenomenon.At high temperature and medium temperature,the temperature stress changes from top to bottom in the panel in the shape of"Z";The vertical deformation is the largest at low temperature,and the pavement structure is the most unfavorable at low temperature when it is only subject to temperature load.Under the coupling action of temperature and load,the stress changes greatly only in the panel,and the buffer layer can prevent the temperature and load transfer to the substructure layer.The warping deformation at high temperature and the compression deformation at low temperature are the largest.In this paper,the response of cement concrete pavement structure with buffer layer is studied,and the comprehensive coefficient of fatigue equation in the code is modified,which can provide theoretical reference for the design and application of this kind of pavement.