重复机车荷载作用下青藏铁路冻土路基累积塑性变形分析

Analysis of cumulative plastic deformation of Qinghai-Tibet Railway subgrade under repeated train loading in permafrost regions

在青藏铁路北麓河试验段选取素填土路基断面,于暖季7月份开展列车通过实时振动测试,获得铁路货运机车振动荷载作用下路肩处的加速度时程曲线。将现场测得的加速度时程曲线作为有限元计算的荷载边界条件,通过非线性动力计算获得路基坡脚和天然地表处的加速度时程曲线,分析机车振动沿路基的传递衰减特性。阐明路基土体内部动应力分布特征和沿深度的衰减规律。应用累积塑性应变模型,对多年冻土路基在重复机车荷载作用下的永久变形进行初步分析和预测。研究结果表明:机车荷载作用所导致的路基变形随着荷载作用次数的增加逐渐趋于稳定。在机车作用1年之后,路基累计变形为27.74 mm,机车作用10年之后,该变形值发展为40.12 mm。

In order to estimate the vibration effect of the train loading, a traditional sand-gravel embankment at the Beiluhe segment along the Qinghai-Tibet Railway was selected, and the strong motion tests were carried out in warm season. The waveforms of acceleration history deduced by the train vibration near railway tracks were collected when train passes, and the typical acceleration history waveform was used as the acceleration boundary condition to simulate the dynamic load effect. By applying the Finite Element Method, the dynamic response of embankment in permafrost region under the train loading was studied, and the transmission and attenuation characteristics of the train loading were obtained. Then the stress ratio of the subgrade soils at different depths was obtained as well. On this basis, the strain accumulation model was applied to study the permanent deformation of the subgrade soils under the influence of repeated train loading. The results show that the permanent deformation deduced by the dynamic load gradually increases with the increase of the times of train load, and the deformation tends to be stable with the increase of time as well. The deformation of subgrade soils deduced by vibration effect under repeated train load in 1 year reaches upto 27.74 mm, while the value could reach upto 40.12 mm in 10 years.