Mechanism And Modeling Of Resilient Modulus Of Cement Treated Base Layer For MEPDG

The resilient modulus influences the mechanical response of the cement treated base under the traffic loads,and is a key design parameter for the design theory of the pavement elastic layered system.Its magnitude directly affects the design results of the pavement structure and the stress of each pavement structure layer.At present,there are two methods to obtain the resilient modulus: the laboratory test and empirical conversion based on 7-day unconfined compressive strength.The process of indoor testing of resilient modulus is cumbersome and time-consuming,and there is a situation in which it does not match the stress state of the on-site base.Due to the influence of factors,it is not suitable for widespread promotion and the design of high-grade highways.Therefore,by analyzing the single variable effect and coupling effect of each influencing factor on the resilient modulus of cement treated base,it is extremely important to develop the high-precision resilient modulus prediction model based on mechanical empirical design method(MEPDG).Based on the project "Characterization of Bases and Subbases for AASHTO ME Pavement Design",this study revealed the deformation characteristics and mechanism of the cement treated base under triaxial dynamic loads,and quantitatively characterized the stress state,material parameters and the law and mechanism of the influence of state variables on the resilient modulus of the cement treated base,the internal relationship between the stiffness and strength of the cement treated base was studied,and the rheological properties of the cement treated base were analyzed and simulated by means of discrete element software.Based on the above research results,prediction models for the resilient modulus of the cement treated base layer under the action of multiple factors are developed.The main research contents and relevant conclusions are as follows:(1)The control variable method is used to study the law and mechanism of the stress state,material parameters and state variables on the resilient modulus of the cement treated base.Aiming at the problem that the maximum loading stress is smaller than the actual working condition,the load combination is revised in this paper,and the revised test method can better reflect the changing law of the elastic modulus.Finally,specimens with different diameters and heights were designed,and the influence law and effect threshold of the size effect on the resilient modulus of the cement treated base were analyzed.(2)In view of the characteristics of the low yield strength of the cement treated base,the dynamic rebound deformation test of the cement treated specimens under different load combinations was carried out,and the law of the elastic and plastic deformation of the cement treated specimens during the loading process was analyzed.Under triaxial loading,the elastic deformation of the stable specimen is dominated by elastic deformation,supplemented by plastic deformation.(3)The compressive strength test of the cement treated base under triaxial loads was carried out,and it was shown that there is a strong nonlinear relationship between the resilient modulus and the compressive strength of the cement treated base.The strengthbased prediction model was used,and the influence of aggregate source,cement content and curing age on the compressive strength of the cement treated base was studied by using the orthogonal analysis method.(4)The application of numerical simulation method further verifies the rheological characteristics of the cement treated base.The results show that the resilient modulus of the cement treated base has a high dependence on the deviatoric stress.(5)By analyzing the single variable effect and coupling effect of each factor on the resilient modulus of the cement treated base,based on the mechanical empirical design method(MEPDG),prediction models of the resilient modulus with different accuracy levels were developed.The low-level accuracy model is established based on cement content,curing age and gradation type,the medium-level accuracy model is based on empirical conversion of compressive strength,and the high-level accuracy prediction model is based on the mechanical model,supplemented by the empirical model.