铁路路基粗粒土填料临界动应力试验研究

Experimental study on critical dynamic stress of coarse-grained soil in railway subgrade

粗粒土填料被广泛应用于铁路基床填料中,直接承受轨道结构传递的列车动循环荷载的长期作用,研究其在列车动荷载作用下的动力行为特征及塑性变形特性可为路基状态评估、沉降控制提供思路。采用GDS动三轴试验系统对铁路基床表层的粗粒土填料动力响应开展研究,通过引入塑性应变率和安定理论,将不同频率、围压、循环动应力比等条件下路基填料的轴向塑性应变的发展规律划分为塑性安定、塑性蠕变和增量塑性破坏3种类型,并确定了塑性安定和塑性蠕变状态的临界动应力水平。研究表明:粗粒土填料的临界循环应力比随着围压的增大而增大,随着荷载频率的增加而减小。通过对试验结果的拟合分析,提出了以围压为变量的临界动应力经验公式,为合理评估列车荷载作用下路基任意深度的动力稳定提供了理论依据。

The coarse-grained soil is widely used as the filling in the railway subgrade,which is directly subjected to the long-term effect of the dynamic cyclic train loads transmitted from the track structure.Investigation of its dynamic behavior and plastic deformation characteristics under the dynamic train loads may provide ideas for the subgrade performance evaluation and settlement control.GDS dynamic triaxial tests were used to investigate the dynamic response of coarse-grained soil in railway subgrade.By introducing the plastic strain rate and shakedown theory,the evolution law of axial plastic strain of subgrade under different frequencies,confining pressures and cyclic dynamic stress ratios is divided into three types:plastic shakedown,plastic creep and incremental plastic failure,based on which the critical dynamic stress levels of plastic shakedown and plastic creep state are determined.Results show that the critical cyclic stress ratio of coarse-grained soil increases with the increase of confining pressure,while decreases with the increase of loading frequency.Based on the fitting analysis of the experimental results,an empirical formula of critical dynamic stress with confining pressure as variable is proposed,which can provide theoretical basis for the dynamic stability evaluation of subgrade at any depth.