Experimental Study On The Elastic-Plastic Deformation Behavior Of Unbound Granular Materials Under Repeated Loading

Compared with the semi-rigid material structure layer of highway pavement,the unbound granular materials(UGM)layer can effectively avoid the occurrence of reflection cracks,with well water stability and drainage performance.It is widely applied abroad as highway pavement base and subbase,but is limited in China because of the large plastic deformation problem.Aiming at the elastic-plastic deformation behavior of UGM,the study conducted repeated loading test via Precision Unbound Materials Analyzer(PUMA),researched the elastic-plastic deformation behavior of UGM under the influence of multiple factors,to provide the basis for the design of unbound granular materials pavement,and to promote the popularization and application of unbound granular materials.Based on the multilayer elastic layered system,considering the influence of the design parameters on the vertical stress of the top surface of the UGM layer,the vertical stress of the inverted pavement structure is between 70~360kPa,the semi-rigid composite base pavement structure is between 15~50kPa,and the flexible base pavement structure is between 45~355kPa.On the basis of the analysis of the composition,principle and confining pressure of PUMA equipment,the comparison between the traditional CBR test,the repeated penetration test and the PUMA test were conducted.The test results showed that the PUMA test was basically consistent with the CBR test and the repeated penetration test results and verified the reliability of the PUMA test method.It is found that the effect of load strength on the elastic-plastic deformation of single particle size gravel is the most significant,and the influence of load frequency and degree of density is more significant.Through the fitting analysis of the plastic strain increment and the number of load repetition,the calculation model of plastic strain increment of the single particle size gravel was established,and the evaluation index of the plastic deformation ability of the gravel,Resistance of Permanent Deformation,RPD,was put forward.Through the PUMA test of two and three filled gravel,it is found that when the particle size is the same,the gravel structure with larger particle size usually has a stronger resistance to plastic deformation,and when larger particle size gravel is filled with each other,the structure resistance to plastic deformation will be reduced to a certain extent because of the interference effect.Through the PUMA test of UGM,it is found that the elastic deformation of the unbound granular materials decreases obviously compared with the single particle gravel,and the effect of the lower load level on the elastic-plastic deformation decreases obviously.With the decrease of the degree of density,the difference of elastic-plastic deformation behavior among different types of UGM decreases gradually.The influence of water content on the mixture is related to the gradation,and the water content corresponding to the maximum anti deformability is generally less than or close to the optimum water content.Based on the research results,a prediction model for permanent deformation of UGM was established,and the model was corrected and verified.