砂土弹性波频散特性试验研究

Experimental study on dispersion characteristics of elastic wave in sand

岩土工程中对频散的试验研究多以正弦脉冲为激励并通过时域法确定波速,操作繁琐,难以大范围、连续地研究土体频散特性,故提出以扫频信号为激励采用频域法研究土体频散的思路。试验使用弯曲元和伸展元在干砂、饱和砂一维固结过程中开展波速测试,以单周期正弦脉冲和扫频信号为激励,采用时域初达波法、互相关法和频域法计算剪切波速、压缩波速并研究它们随频率的变化,评估三种方法的合理性。结果显示互相关法、频域法测得的频散特性基本一致,但与时域法结果差异较大。对正弦脉冲接收信号波形进行时频分析表明以扫频为激励的频域法结果比时域法更加合理。由频域法波速绘制频率-波数曲线研究砂土中横波、纵波的频散特性。试验表明武汉砂中横波、纵波的频散均对荷载不敏感,横波频散程度较小,且在干砂和饱和砂中区别不大,纵波频散程度较大,在饱和砂中有所降低。

In the experimental study on wave dispersion insoil,sinusoidal pulse is often used as the excitation and the wave velocity is determined by the time domain method.However,the operation is usually too complicated to continuously acquire the dispersion characteristics of a soil over a large scale.A frequency domain method was proposed in this study with a frequency sweep signal.The wave velocity was measured in one-dimensional consolidation test of dry and saturated sand using bender-extender elements.The sand sample was excited by a single-period sinusoidal pulse and frequency sweep signal.Three methods,i.e.time-domain first arrival method,cross-correlation method,and frequency-domain method,were used to calculate the shear and compression wave velocities.The results show that the dispersion characteristics measured by the cross-correlation method and the frequency domain method are different from the same,but the results of the time domain method.In terms of time-frequency analysis on the received signal of sinusoidal pulse,it was found that the frequency domain method with frequency sweep signal as excitation is more reasonable.The dispersion of shear and compression wave is not sensitive to the external loading.The degree of dispersion of shear wave is subtle,and little difference was found between dry and saturated sand.The degree of dispersion of longitudinal wave is relatively prominent in dry sand,yet considerably reduced in saturated sand.