分级循环荷载作用下冻土动应变幅值的试验研究

Experimental study of dynamic strain amplitude of frozen soil under stepped axial cyclic loading

通过低温动三轴试验,采用分级加载方式逐级施加动荷载,对不同加载频率、围压和负温条件下青藏冻结黏土和兰州黄土的动应变幅值变化特征进行了试验研究。结果表明,同一级荷载作用下,动应变幅值随振次的增加基本不变,可以采用平均值来反映各级加载下的动应变幅值;不同加载频率、围压和温度条件下,动应变幅值随动应力幅值的变化规律相同,即随着动应力幅值的增加,动应变幅值逐渐增大;动应变幅值随加载频率的增加而减小,但减小的速率逐渐降低,动应变幅值最终趋于一稳定值,对于青藏黏土和兰州黄土,该稳定值均随加载级数的增加而增加;随着围压的增加,青藏黏土的动应变幅值变化不大,而兰州黄土的动应变幅值呈逐渐减小的趋势;动应变幅值随温度的降低而减小。动应力幅值对动应变幅值的影响最大,动荷载振动频率的影响次之,温度的影响第三,围压的影响最小。

Dynamic triaxial test is performed to study dynamic strain amplitude of Qinghai-Tibet frozen clay and Lanzhou loess under staged dynamic loading with different loading frequencies, confining pressures and negative temperature conditions. The results show that the dynamic strain amplitude is basically unchanged with increasing vibration cycles under the same load level; and average values are used to characterize dynamic strain amplitude. The law of that dynamic strain amplitude changes with dynamic stress amplitude are the same; namely dynamic strain amplitude increases with increasing of dynamic stress amplitude with different loading frequencies, confining pressure and negative temperature conditions. Dynamic strain amplitude decreases with increasing of loading frequencies, but the decreased rate is becoming more and more small that it tends to be a stable value, which increases with the increasing of loading series. With increasing of confining pressure, dynamic strain amplitude for Qinghai-Tibet clay is basically unchanged and for Lanzhou loess decreases gradually. Dynamic strain amplitude decreases with decreasing temperature. The most important effect on dynamic strain amplitude is dynamic stress amplitude, vibration frequencies of dynamic load secondly, temperature thirdly, and confining pressure with minimal impact.