Research On Characteristics Of Dynamic Resilient Modulus Of Graded Crushed Rock Stiffness Transition Layer

Based on the new structural design idea of durable asphalt pavement with the design life of structural layer increasing from the surface layer to the subbase course,the idea of setting up a graded crushed rock transition layer with certain thickness and rigidity between the subgrade and semi-rigid base was proposed.It would exert the compensating and transitional influence of graded crushed rock layer on the subgrade stiffness,and give play to coordinating effect on the stress and deformation of asphalt pavement structure as well.Due to the nonlinear characteristics of mechanical properties of graded crushed rock materials,the mechanical properties of graded crushed rock were of high stress dependence.The stress state of graded crushed rock layer would be influenced by the load grade and action mode.The mechanical property parameters of graded crushed rock materials were different under different stress state,so the results of mechanical response of pavement structure were different accordingly,which would directly affect the scientificalness and accuracy of the structure design of durable asphalt pavement.Therefore,the mechanical properties of graded crushed rock would be studied by the means of the dynamic tri-axial test in this thesis.And the determining method and range of resilient modulus of graded crushed rock stiffness transition layer were put forward.According to the gradation range of graded crushed rock in the current specifications for highway asphalt pavement design in China,the design gradation of the skeleton dense structure were also determined by construction process in the actual engineering.The optimum moisture content and maximum dry density of the graded crushed rock materials were determined by the heavy compaction method.In order to simulate the material in the most unfavorable condition in the process of use,the CBR strength tests were carried out under different saturated water time.The results had showed that the saturation of 24 h was the most unfavorable state.The dynamic resilient modulus test of graded crushed rock was carried out by thedynamic tri-axial test equipment.The analysis showed that the maximum aggregate size,moisture content,compactness,stress,confining pressure,and the first stress invariant had influenced the dynamic resilient modulus.And,the results also showed that resilient modulus with increasing stress would increase the confining pressure,the first stress invariant,the compactness,the maximum aggregate size gradually increased while and decrease the moisture content,and the main reasons were analyzed and the technical proposal were provided.The dynamic resilient modulus and static resilient modulus were compared and analyzed,which results showed that the fixed stress state of the static resilient modulus was not matching the dynamic stress state of the actual pavement.According to the dynamic resilient modulus test results of different physical properties,the constitutive models of the commonly used granular material resilient modulus were fitted,and used to carry on the contrast analysis.The nonlinear model of resilient modulus of graded crushed rock material was determined,which was the fittest the skeleton dense structure.Based on this model,the range of modulus value of graded crushed rock stiffness transition layer of the durable asphalt pavement,of which the structural layer design life increases from the surface layer to the subbase course,was put forward.Research results could be provided as a reference for the reasonable value of design parameters.