Study On Strain And Dynamic Characteristics Of Saturated Remoulded Loess Under Cyclic Traffic Load

With the increasing of traffic infrastructure and widening subgrade projects in Northwest China,loess,as the most common subgrade material,bears the long-term and complex cyclic load-traffic load which causes the accumulation of axial strain and changes of stiffness in varying degrees.These changes lead to different degrees of settlement of subgrade soil,irregular cracks and ruts of pavement,etc.In highway widening engineering,the difference of the history between the new and old subgrade subjected by traffic loads,is one of the reasons for uneven settlement,which causes irregular settlement between the new and old subgrade.Therefore,the GDS hollow cylindrical torsional shear apparatus is used in this paper to study the characteristics of soil under the condition of heart-shaped path cyclic traffic load with 100 kPa effective stress.The details are as follows:?1?By controlling the Cyclic vertical stress ratio?CVSR?and Torsion-shear stress ratio???of cyclic traffic load under the drained condition,the axial strain?_z has a positive correlation with CVSR and?.The radial strain?_r increases in the negative direction,then,it increases in a positive direction and finally tends to be stable;the circumferential strain?_?and the shear strain?_z?increases in the negative direction,but the strain value is small.The change law of octahedral shear strain is basically similar to that of?_z.After 100 cycles,the specimens reach plastic-stability stage.?2?According to the vertical strain index-model proposed by Monismith et al.,introducing two influencing factors of CVSR and?,the Vertical Strain Prediction Model under Traffic Load is constructed by undetermined parameter method.Meanwhile,compared model I proposed with the predicted vertical strain accumulation model without considering the rotation of the principal stress axis proposed by Puppala et al.,the experimental data has smaller difference with the former model,which means it can predict the vertical strain accumulation of the sample better.?3?The dynamic shear modulus of the sample is between 20MPa and 30MPa.Under the first 100 cycles of cyclic traffic load,the dynamic shear modulus decreases sharply,and then,it tends stable.The resilient modulus is between 50MPa and 100MPa.When?=0,the sample is not subjected by the torsional shear load,and the resilient modulus gradually increases with the number of cycles.When??0,the sample is subjected to torsional shear stress under cyclic traffic load,the principal stress axis rotating continuously,the resilient modulus decreasing rapidly at the beginning of the test,and then remain stable.?4?Under dynamic loads,the direction of stress and strain increment is obviously different,that is,there is obvious non-co-axiality.The laws of non-coaxial angle change are similar in different loading times,CVSR or?.The analysis of dissipation energy shows that under drained condition,the dissipation energy caused by?_z and?_r is negative under traffic load,that is to say,it can reinforce the specimen.The dissipated energy caused by?_?is very small and has little effect on the damage of soil elements.W_?z?accumulates in the positive direction and has a larger value,which indicates that the?_z?has a greater impact on the damage of the specimen.