列车荷载下考虑频率影响的软黏土破坏标准研究
Failure criteria for soft clay subjected to frequencies under train loads
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摘要: 列车荷载在地基土体中引发一种心形线主应力轴旋转动力路径,考虑频率作用时,会对地基土产生更为复杂的影响。以南京河西典型重塑软黏土为对象开展数组不同频率f和动应力比η的不排水空心扭剪试验。试验发现,不同动应力比下,土体变形随振动频率的变化趋势主要分为两种情况。另外,随着频率f的提高,试样发生破坏的临界动应力比先减小后增大。频率f在1.0~2.0 Hz范围内,孔压发展曲线受频率影响较小,当f=0.5 Hz时,孔压发展显著增大。提出一种适用于列车荷载下考虑频率影响的重塑软黏土破坏评价方法。该标准以孔压-应变耦合曲线为主要辨识曲线,可以判别试样所属的稳定、临界或破坏型状态,为后续开展列车荷载引起的软黏土地基承载力研究提供理论支持。Abstract: The heart-shaped stress path can be caused by train loads in the foundation. The train load path has a more complicated influence on foundation soils when the effects of frequencies are considered. A serious of undrained cyclic hollow torsional shear tests are carried out on typical remold soft clay (in Hexi District of Nanjing) with different values of vibration frequency f and dynamic stress ratio η. It is found that the trend of soil deformation influenced by frequencies can be divided into two types. Otherwise, the critical dynamic stress ratio first decreases and then increases with the increase of the frequency. When the frequency f locates in the range of 1.0~2.0 Hz, the developing curves of pore pressure are consistent and the influences of the frequencies are small. However, when the frequency equals to 0.5 Hz, the development of pore pressure significantly increases. Then a new failure evaluating method for remolded soft clay is presented. It is used to investigate the influences of the frequencies caused by train loads. This criterion can distinguish the stable, critical or destructive states of samples mainly by the pore pressure-strain coupling curve. The range of failure strain and vibration cycles can also be given. The results may provide theoretical support for the researches on the bearing capacity of soft clay foundations subjected to traffic loads.