双向动荷载下振动频率对黄土动力特性的影响

Effect of vibration frequency on dynamic characteristics of loess under bidirectional cyclic loading

采用TYS-20型电脑控制电液伺服土动三轴试验机对Q3黄土试样进行了一系列的动三轴试验,探究了双向循环荷载作用下振动频率对黄土动力特性的影响。动强度试验结果表明:当振动频率在0.2~3 Hz范围内变化时,黄土的动强度随振动频率f的增大而增大;对动强度与振动频率的关系在双对数坐标系上进行拟合发现:相同破坏振次下,两者近乎呈直线关系;在破坏振次分别为10,20,30次条件下,频率0.2,1 Hz相比3 Hz得到的动强度相对降低值最大可达到61.9%,最小为11.9%,且围压越小,降低程度越明显。动模量试验结果表明:动剪切模量随动剪切应变的增大而先增大后减小,在衰减过程中,频率越大衰减越缓慢,同一动剪切应变对应的动剪切模量也越大;在相位差为0°条件下,振动频率越小动剪切应变发展越快,侧向循环应力幅值的增大减慢了土体动剪应变的发展速度,在一定范围内侧向循环应力幅值越大越有利于土体稳定。

Computer-controlled（ TYS-20） electrohydraulic servo tester was used in the dynamic triaxial tests on loess Q3 to research the influence of vibration frequency on loess s dynamic characteristics under bidirectional load. The dynamic strength tests show that the loess＇ s dynamic strength climbs with the rise of vibration frequency in the range from 0. 2 to 3 Hz. Under the same failure cyclic number,a linear relation is found between the dynamic strength and vibration frequency in the dual-logarithm coordinate system. Under the failure cyclic number of 10,20,30,and the frequency of 0. 2,1. 0,3. 0 Hz,the relative reduction value of the dynamic strength can reach the highest of 61. 9% and the lowest of 11. 9%,and the smaller the confining pressure is,the more obvious the decreasing degree appears. The results show that the dynamic shear modulus goes up at first and then falls with increase of the dynamic shear strain,and the fallen trend goes slower with increasing vibration frequency during the decay process of the dynamic shear modulus. The dynamic shear modulus increases with vibration frequency rising under the same dynamic shear strain condition. When the phase difference is 0°,the development of dynamic shear strain speeds up at low vibration frequency. The increase of the lateral cyclic stress amplitude slows down the development of the dynamic shear strain,so the soil gets stable when the lateral cyclic stress amplitude rises.