Experimental And Theoretical Study On Cumulative Deformation Of Unsaturated Silt Roadbed Fill Under Long-term Traffic Loadings

With the development of China’s transportation strategy,to ensure the safety,sustainability and practicality of roadbed engineering,roadbed engineering problems such as roadbed settlement deformation and road rutting need to be solved.The excessive accumulated deformation of roadbed under millions of traffic loads is the direct cause of roadbed engineering diseases.Therefore,the study of the mechanism of plastic deformation of roadbed,and on this basis to predict the development trend of plastic deformation of roadbed and allowable bearing capacity,for the prevention of roadbed engineering disease is of great significance.In view of this,this paper uses indoor tests and theoretical analysis as the research means to carry out the research on the static characteristics and accumulated deformation characteristics of the roadbed powder filler,combines them with the stability theory,establishes the plastic stability limit criterion of the roadbed powder filler,further establishes the cumulative plastic strain prediction model of unsaturated powder soil and the ultimate plastic stability stress prediction model,so as to improve the roadbed powder filler stressstrain prediction model under the action of long-term traffic load.The safety evaluation index of the stress-strain of the filler under long-term traffic load is improved.The main contents,methods and results of this paper are as follows.(1)Using the roadbed powder fill as the test object,the foundation physical properties test,soil-water characteristic curve test and static and dynamic triaxial tests were conducted to study the effects of surrounding pressure and water content on the static strength of the roadbed powder fill,and the variation law of the accumulated strain of the roadbed powder fill under different surrounding pressure,water content and dynamic stress amplitude,and the relationship function of soil-water characteristic curve was derived.(2)By combining the results of dynamic triaxial tests with the stability theory for the long-term traffic loadings,the stability behavior is classified based on the trend of the accumulated strain rate,and the specimens with different stability behaviors are screened out,and the accumulated strain rate and the slope of the secondary cyclic compression stage of these specimens are statistically summarized according to the different stability behaviors,so as to obtain the plastic stability limit criterion of the road base powder fill characterized by the accumulated strain rate and the slope of the secondary cyclic compression stage,respectively.(3)Based on the plastic stability limit criterion,the ultimate plastic stability stresses of the specimens under different surrounding pressure and different moisture content conditions were determined,and the influence of surrounding pressure and matrix suction on the ultimate plastic stability stresses was further studied and analyzed.Then,following the strength theory of unsaturated soil,the corresponding molar circles are drawn by the matrix suction,the surrounding pressure and the corresponding ultimate plastic stability stress,and the envelope equations corresponding to the ultimate plastic stability states under different matrix suction and surrounding pressure are established respectively,and the two are combined to obtain a prediction model of the ultimate plastic stability stress of unsaturated powder soil considering the coupling effect of surrounding pressure and matrix suction.Finally,the prediction model is validated using experimental results.(4)By combining the existing cumulative strain prediction model with the unsaturated soil strength theory,the shear strength index is firstly derived based on the static triaxial shear test data,and then the static strength expression is further introduced.Then,the cumulative deformation data of the specimens were introduced and normalized by combining the plastic stability criterion,and the data were then fitted and analyzed to obtain the parameter values and ranges to obtain the cumulative strain prediction model for unsaturated powder soils.