侧装式弯曲元测量软黏土剪切波速的试验研究

Determination of shear wave velocities of soft clay samples using side-mounted bender elements

判断剪切波到达时间并计算相应的剪切波速是弯曲元试验的关键问题之一。受到试验仪器差异和研究者波速判断主观性的影响,很难客观地、准确地获得土体的剪切波速。针对该问题,提出采用侧装式弯曲元测试系统测量剪切波传播时间和土体的剪切波速,利用上海典型的淤泥质黏土进行试验,分别采用初达波法、特征值法和互相关法计算土体的剪切波速。试验结果表明,(1)初达波法在信号判定过程主观性较大,土体剪切波速受发射信号频率的影响明显;(2)采用第二峰值点(特征点法)得到的试验结果波动性较小;(3)在满足相似性的前提下,互相关法在一定频率范围内(20~30 k Hz)提高了确定剪切波速的客观性,降低了因试验者或激发频率的不同对试验结果产生较大影响的可能性。

In a bender element test, the most key problem is associated with the determination of travel time of shear waves. The objective and accurate measurement of shear wave velocities remains a challenge. A new side-mounted bender element testing system in which each set of bender elements consists of one transmitter and two receivers has been developed. Bender element tests are carried out on Shanghai soft clay by using the newly-developed system. Three different methods, i.e., first arrive time method, peak-peak method and cross-correlation method are used to calculate the shear wave velocities. The test results show that the first arrive time method is the most subjective method and the shear wave velocities are highly dependent on input frequency. Picking the second peaks of received signals gives rise to consistent shear wave velocities. Cross-correlating two received signals generates most objective and consistent shear wave velocities in the frequency range of 20-30 k Hz provided the similarity requirement is fulfilled.