熔融石英粒径对透明土位移测量精度的影响

Influences of grain sizes of fused quartz on displacement measurement accuracy of transparent soil

利用透明土技术和激光散斑图像结合数字图像相关方法(DIC方法)测量土体内部的位移场,是研究土力学问题的一种新方法。通过试验研究不同粒径范围的熔融石英颗粒(中细砂0.1~0.3 mm、中砂0.3~0.5 mm、粗砂0.5~2 mm、细砾2~5 mm),揭示粒径对激光散斑图像质量、DIC查询窗口和位移场测量精度的影响。结果表明,不同粒径的熔融石英透明土模型产生的散斑场图像、灰度直方图明显不同;相同入射激光下,小粒径比大粒径模型获得更好质量的散斑图像。位移误差直方图显示,位移误差依赖于查询窗口尺寸和颗粒大小。通过平均灰度梯度调整查询窗口,不同粒径的透明土模型可以给出彼此相当的测量精度。数字和物理平移试验显示,由小粒径石英颗粒配置的透明土模型能够得到更高的测量精度。

Laser speckle image of transparent soil, which is a novel method for studying the soil mechanics problems, can be used to measure the displacement field inside the soil mass through digital image cross correlation（DIC） method. Tests are conducted on fused quartz particles with four different grain sizes, i.e. fine quartz（0.1-0.3 mm）, medium quartz（0.3-0.5 mm）, coarse quartz（0.5-2.0 mm）, and fine gravel quartz（2-5 mm）. This paper reveals the influences of grain sizes of fused quartz on the quality of laser speckle image, the selection of appropriate query window size and the displacement measurement accuracy of transparent soil. The results show that the gray histograms and the speckle patterns are different for transparent soils of different grain sizes. With the same incident laser light, the quality of image for smaller sizes is better than that of the larger sizes. The histograms of obtained displacement error indicate that the displacement error is dependent on the query window size and grain size. By adjusting the query window size with the average gray level gradient, the transparent soil models of different grain sizes can provide the equivalent measurement accuracy. Digital and physical translation tests show that the transparent soil models of smaller sizes tend to give higher measurement accuracy.