Research On The Development Of Structure And Material Performance Of Semi-rigid Base

Semi-rigid base layer is the main bearing layer of the pavement structure because of its high strength and stiffness.It is widely used in expressway pavement structure in China.However,under the action of driving load,the base is subjected to repeated fatigue of bending and tension stress in the direction of driving.Because of the repeated action of loading and the decay of its own performance,micro-cracks are generated and expanding in its interior,and fatigue cracks will occur when the cumulative damage exceeds the ultimate tensile fatigue limit,which will affect the service quality of highway.Therefore,evaluating the current performance of semi-rigid base and studying its long-term performance development law are the foundation and important work to improve the durability of pavement structure,and it can also provide some basis for improving the design and construction level of semi-rigid base.Firstly,this paper establishes the finite element model of the deflection basin of typical pavement structure,calculating the theoretical value of the deflection basin parameter D₂₀-D₆₀under different modulus combinations.That the deflection basin parameter D₂₀-D₆₀ has a strong correlation with the base modulus is verified in this paper.It is determined that D₂₀-D₆₀ is a macroscopic evaluation index of the bearing capacity of semi-rigid base.Based on the data of typical high-speed historical deflection basins in Jiangsu Province,the changes of D₂₀-D₆₀ are analyzed,and the main factors affecting the development of bearing capacity of base course are studied.Secondly,based on the factors of road age,traffic volume,materials of base layer,pavement structure and disease,the unconfined compressive strength,compressive resilience modulus and dynamic modulus tests are carried out on the base of typical Expressway sections in Jiangsu Province.The results of the tests are compared and analyzed,and the compressive strength is determined as the mechanical performance evaluation index of semi-rigid base material,and the value of dynamic modulus is proposed as the structure modulus of base layer;Ground Penetrating Radar?GPR?is used to detect the base layer in the coring position,and the performance of semi-rigid base is analyzed from the perspective of slab properties.Thirdly,the existing fatigue tests of semi-rigid base are studied,and the stress characteristics are analyzed and compared.And then a set of semi-circular bending test method of semi-rigid material is proposed referring to asphalt mixture fatigue test.The splitting strength and fatigue test of base core sample are carried out,and the fatigue curves under different guarantee rates based on semi-circular bending fatigue test are obtained.Besides,the strength and fatigue properties of semi-rigid materials were observed by scanning electron microscopy?SEM?,and the mechanism of the strength and fatigue properties of semi-rigid materials was studied from the view of microcosmic.Finally,the finite element model of pavement structure is established,and the influence of modulus and thickness parameters on the tensile stress of base layer is studied by changing the values of modulus and thickness of structure layers.Combining with the material fatigue curves based on semi-circular bending test,the structure fatigue model of semi-rigid base layer with unconfined compressive strength as index is established through the test results of modulus and strength.