寒区铁路冻结粗粒土填料长期变形特性研究

Long-term Dynamic Characteristics of Frozen Coarse-grained Materials of Railway in Cold Regions

振动列车荷载长期循环往复作用下土体产生的变形存在一定程度的应变累积,依托某寒区铁路,开展不同温度下冻结粗粒土填料长期动三轴试验,探究填料长期变形、弹性模量和阻尼比的变化规律,并对试样累积塑性变形进行安定性分析,将累积塑性变形划分为三种不同的状态。在黏弹性模型的基础上串联塑性弹簧提出一种计算应力-应变关系的简化方法。研究结果表明:温度越低,动弹性模量越高,阻尼比越低。在动应力水平较低时,土体处在塑性安定阶段,累积塑性变形随振动次数的增加趋于稳定,动弹性模量略有增加,阻尼比则逐渐减小;当动应力水平超过塑性蠕变界限时,土体刚度迅速降低,累积塑性变形急剧增加,试样呈现破坏的趋势;当动应力水平处于塑性安定和塑性蠕变界限之间时,累积塑性变形虽然增加,但仍然处在可控范围。提出的弹塑性模型可以很好地描述冻结粗粒土填料的滞回特性和累积塑性变形规律。研究成果可为高速铁路路基填料长期动力性能的分析提供有益参考。

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 temperatures 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 model 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 plastic shakedown limit,the soil stiffness decreases rapidly with the cumulative plastic deformation increasing sharply,resulting 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 increases,it is still in a controllable range.The elastoplastic model presented in this paper can describe the hysteretic characteristics 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.