多频段循环荷载下海洋黏土动力特性试验研究

Experimental study on dynamic characteristics of marine soil under multi-frequency loading

为探究海洋土的动力特性及动力影响因素,采取原状黄海海洋黏土,利用GCTS动三轴试验系统开展室内试验研究,探讨偏应力水平、动应力幅值和动荷载频率对海洋土动应力应变关系和动孔压的影响规律,分析动剪切模量和阻尼比的变化特征。试验结果表明:海洋黏土的动应变随偏应力水平提高和动应力幅值增大而增大,且具有显著的频率效应,低频段动荷载(0.02~0.1 Hz)引起的动应变累积量高于高频段动荷载(1~10 Hz)的应变累积量;在低频段动荷载作用下,土样内超静动孔压显著上升,而在高频段下,动孔压的累积变化量很小;土样的动剪切模量对动荷载的频率反应不十分明显,仅在低频段,动剪切模量会随动荷载频率的提高略有下降,但是会随动应力幅值增加而显著提高,随偏应力水平提高而显著下降;土样的阻尼比对动荷载频率也很敏感,在低频段,阻尼比随频率的增大而降低,在0.1 Hz时的阻尼比最低;在高频段,土样的阻尼比随动荷载频率增加明显提高,提高幅度可达到1倍以上;阻尼比会随动应力幅值增长而略有减小,随偏应力水平提高而略有增加。

In order to explore the dynamic characteristics of marine soil and their dynamic influential factors,the laboratory dynamic triaxial tests are carried out on the undisturbed marine soil from an investigated site in Yellow Sea,China by using the GCTS dynamic apparatus.The influences of the deviator stress,dynamic stress amplitude and dynamic load frequency on the dynamic stress-strain behavior and dynamic pore pressure of the marine soil are discussed,and the variation characteristics of dynamic shear modulus and damping ratio are analyzed.The test results show that the dynamic strain of the marine soil increases with the increase of the deviator stress and dynamic stress amplitude,and that the behavior of the marine clay is significantly affected by the loading frequency,i.e.,in the low frequency band(0.02~0.1 Hz)of loading,the dynamic strain accumulation is much higher than that happens in the high frequency band(5~10 Hz)of loading.The excess pore water pressure increases sharply during low frequency loading cycles,but within the high frequency of loading,it is scarcely accumulated.The dynamic shear modulus of the marine clay exhibits weak response to the frequency of dynamic loading,i.e.,within the low frequency band of loading,the dynamic shear modulus drops a little with the frequency transition,and it increases with the increase of the dynamic stress amplitude and decreases with the increase of the deviator stress level.In the high frequency band(1~10 Hz),the damping ratio of the soil samples increases significantly with the increase of the dynamic load frequency,and the increase range can reach more than 1 time.The damping ratio decreases slightly with the increase of the dynamic stress amplitude,and increases slightly with the increase of the deviator stress level.