Interface Effect Of Layered Roadbed And Its Application To Damage Assessment In Operation Period

Most of the highways in our country are built on the layered roadbed with different soil properties overlapped each other.Under the influence of traffic load,a dynamic mutagenesis occurs at the interface of layered roadbed,which is called interfacial effcet.When the mechanical properties of the upper and lower soil layers are quite different,the layered roadbed will produce relative sliding or cracking due to the influence of interface effect.In the most of current research on damage and deformation of roadbed,roadbed is usually regarded as a single layer,and the interfacial effect is ignored.This paper starts with the mechanical properties of the interface layer,analyzes the influence of interface effect in layered roadbed when the mechanical properties of interface layer change,and discusses engineering application of damage evaluation of layered roadbed in operation period.Through indoor direct shear test,different factors of normal stress and shear position of soil layer,the remolded soil with different factors of type of upper and lower soil layer,interface treatment,normal stress,shear position of soil layer and disturbance duration were analyzed,founding that the mechanical properties of the interface soil are related to the treatment of the interface,the mechanical properties of the upper and lower soil layers and the disturbance time of the external load.The shear bond coefficient of interface soil is obtained to evaluate the interface effect of layered roadbed.Based on the indoor direct shear test,BISAR 3.0 was used to calculate the influence of four different factors of soil layer setting,interface bonding mode,propagation distance and traffic load type on the interface effect when the layered roadbed was subjected to a traffic load,and the influence degree of these four factors is sorted.Secondly,when the layered roadbed is subjected to the cyclic traffic load,the interface bonding mode has a great influence on the characteristic strain of the interface soil of the upper roadbed and the interface soil of the lower roadbed.By using FLAC3 D and setting the relationship between the normal and tangential bond coefficients,the results show that the interface effect of layered roadbed is affectedBy the change of normal and tangential adhesion coefficient.The influence of the change of normal bond coefficient on the interface effect is more intense.Taking two-layer roadbed covering natural hard crust as the research object,a nonlinear fatigue cumulative damage model was put forward to evaluate the dynamic damage characteristics of two-layer roadbed based on the theoretical derivation and the data of engineering examples and dynamic triaxial tests.By means of data statistics,the evolution information of roadbed damage was analyzed,and the design index basis of layered roadbed in operation period is given.