粉质砂土剪切波速测定的弯曲元试验

在天然状态下砂土中常含有粉粒或黏粒。采用人工配比砂土与硅粉的方法,进行了不同密实度和不同围压下的弯曲元试验,通过对比剪切波输出信号,重点分析了激振频率以及含粉量对波形特征的影响,获得了可靠的剪切波传播时间确定方法。研究结果表明:(1)在低频激振条件下,粉质砂土输出波近场效应明显;在高频条件下,第一类P波出现,其振幅与试样的含粉量相关,综合分析实验结果,发现采用初达波方法判断剪切波的传播时间比较可靠;(2)在相同的孔隙比和围压下,随着含粉量由0增加到30%,试样的剪切波速逐渐减小;(3)基于临界状态土力学理论,提出了计算粉质砂土剪切波速的多参数归一化模型,与传统方法相比,模型中各拟合参数不受含粉量影响,计算过程更简便。

Experimental Study on Shear Wave Velocity of Silty Sand Using Bender Element

Natural sands are not clean but contain some fines of silt or clay size. In this study, a series of bender element tests has been carried out on mixtures of clean quartz sand and crushed silica fines of different mass contents, covering a range of confining stresses and void ratios. Discussions were made with focus on the influences of excitation frequency and fines content on the output signals. A reliable measure of the first arrival time of shear wave was achieved. It is found that (1) at low excitation frequency the near field effect is prominent for silty sand. On the other hand, the first-kind P wave appears at high excitation frequency, whose amplification is of great dependence on the fines content. Accordingly, the shear wave velocity can be calculated using the first arrival in the time domain; (2) when the fines content increases from 0 to 30%, the shear wave velocity decreases progressively under otherwise similar conditions; (3) a unified model based on critical state soil mechanics is superior to the conventional method in characterizing the influence of various factors.