Long-term Dynamic Characteristics of Frozen Coarse-grained Materials of Railway in Cold Regions
A certain degree of strain is accumulated in the deformation of soil under the long-term cyclic of vibrating train load.Relying on a railway in a cold region,long-term dynamic triaxial tests were carried out at different tempera-tures on frozen coarse-grained materials to study the changes in the long-term deformation,elastic modulus and damping ratio of the materials.By dividing the cumulative plastic deformation into three stages,the stability of the cumulative plastic deformation of the samples was analyzed using the shakedown concept.On the basis of the viscoelastic model,a simplified method was presented to calculate the stress-strain curve by connecting a plastic spring to the viscoelastic mod-el in series.The results show that the lower the temperature,the higher the dynamic elastic modulus and the lower the damping ratio.At low dynamic stress level,the material behaves in a manner corresponding to the plastic shakedown range.The cumulative plastic deformation tends to be stable with the increase of vibration frequency.The dynamic elastic modulus increases slightly,while the damping ratio decreases gradually.When the dynamic stress level exceeds the plas-tic shakedown limit,the soil stiffness decreases rapidly with the cumulative plastic deformation increasing sharply,resul-ting in a trend of failure of the samples.When the dynamic stress level locates between the elastic shakedown limit and plastic shakedown limit,the elastic modulus and damping ratio change little.While the cumulative plastic strain increa-ses,it is still in a controllable range.The elastoplastic model presented in this paper can describe the hysteretic charac-teristics and cumulative plastic deformation of frozen coarse-grained materials.The results can provide useful reference for the analysis of long-term dynamic characteristics of coarse-grained embankment materials in high-speed railway.
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